Showing papers by "University of Maryland, Baltimore County published in 1988"

Influence of Positive Affect on the Subjective Utility of Gains and Losses: It Is Just Not Worth the Risk

Abstract: A modification of the procedure originally used by Davidson, Suppes, and Siegel (1956) to measure subjective utility was used to study the influence of positive affect on individuals' perceived value (utility) functions. Results indicated, as expected, that persons in whom positive affect had been induced showed a more negative subjective utility for losses than did controls. This indicates that losses seem worse to people who are feeling happy than to those in a control condition. The subjective utility functions of the two groups did not differ as much, however, when people were considering potential gain. Thus, at least in the situation tested in this study, potential gains did not seem to be more appealing (nor less so) for affect subjects than they did for controls. These findings are discussed in relation to theoretical issues in decision making and work suggesting that positive affect can promote increased sensitivity to losses in situations of potential meaningful loss.

A Survey of Medication Treatment for Hyperactive/Inattentive Students

Abstract: Since 1971, the Baltimore County Health Department has conducted nine biannual surveys of school nurses in all of the county's public and private schools to determine the prevalence of medication treatment for hyperactivity/inattentiveness among students. The results reveal a consistent doubling of the rate of medication treatment for hyperactive/inattentive students every four to seven years such that in 1987,5.96% of all public elementary school students were receiving such treatment. Related trends from 1971 to 1987 have been that stimulants increased from 76% to 99% of the medication prescribed; methylphenidate hydrochloride rose from 40% to 93% of the total; the male-female ratio dropped from an average of 8:1 to 5:1; the rate of medication treatment for hyperactive/inattentive students rose faster in secondary than in elementary schools; and 25% of students receiving stimulant medication in 1987 were in special education classes or schools. ( JAMA 1988;260:2256-2258)

Functional recovery and medical costs of trauma: an analysis by type and severity of injury.

Abstract: This study was designed to delineate the factors that influence the extent and rate of recovery as related to the characteristics and duration of functional limitations resulting from trauma. The study population was 597 surviving trauma patients aged 16-45 years from two trauma centers in a single state system which follow similar care protocols, and included patients with extremity, abdomen, thorax, brain, and spinal cord injuries. Of 479 trauma patients (80% of the total) who were followed for a full year, 57% had no activity restrictions, 16% had some limitation with either a major or minor physical activity, but did not have any difficulty with mobility or self care, and 27% were limited in either mobility or one of the five basic self-care activities. Further analyses show that of the 262 individuals who were working full-time before the injury, 57% had actually returned to full-time employment within the year. Factors in addition to type and severity of trauma that influence return to work were higher educational level, white collar employment, higher preinjury income, and the presence of supportive individuals among family or friends. Recovery as defined by functional status and return to full-time work is analyzed by body region and severity of the principal injury sustained.

Social support, organizational characteristics, psychological well-being, and group appraisal in three self-help group populations

Abstract: This study examined the relationship of three social support and three organizational variables to two well-being and two group appraisal variables among 144 members of Compassionate Friends, Multiple Sclerosis, and Overeaters Anonymous self-help groups. An anonymous questionnaire was the major research instrument. Receiving social support was not significantly related to depression or anxiety but was positively related to perceived group benefits and group satisfaction. Providing social support and friendship were each positively related to one well-being and one group appraisal variable. Bidirectional supporters (i.e., individuals high on both receiving and providing support) reported more favorable well-being and group appraisal than Receivers, Providers, and Low Supporters. At the group level of analysis (n = 15 groups), groups with higher levels of role differentiation, greater order and organization, and in which leaders were perceived as more capable contained members who reported more positive well-being and group appraisal. The implications for future research and professional consultation to self-help groups are discussed.

The engineering of binding affinity at metal ion binding sites for the stabilization of proteins: subtilisin as a test case.

Abstract: A weak Ca/sup 2 +/ binding site in the bacterial serine protease subtilisin BPN' was chosen as a model to explore the feasibility of stabilizing a protein by increasing the binding affinity at a metal ion binding site. The existence of this weak Ca/sup 2 +/ binding site was first discovered through a study of the rate of thermal inactivation of wild-type subtilisin BPN' at 65/degrees/C as a function of the free (Ca/sup 2 +/). Increasing the (Ca/sup 2 +/) in the range of 0.10-100 mM caused a 100-fold decrease in the rate of thermal inactivation. The data were found to closely fit a theoretical titration curve for a single Ca/sup 2 +/ specific binding site with an apparent log K/sub a/ = 1.49. A series of refined X-ray crystal structures of subtilisin in the presence of 0.0, 25.0, and 40.0 mM CaCl/sub 2/ has allowed a detailed structural characterization of this Ca/sup 2 +/ binding site. Negatively charged side chains were introduced in the vicinity of the bound Ca/sup 2 +/ by changing Pro 172 and Gly 131 to Asp residues through site-directed and random mutagenesis techniques, respectively. These changes were found to increase the affinity of the Ca/supmore » 2 +/ binding site by 3.4- and 2-fold, respectively, when compared with the wild-type protein. X-ray studies of these new variants of subtilisin revealed the carboxylate side chains to be 6.8 and 13.2 /Angstrom/, respectively, from the bound Ca/sup 2 +/. These distances and the degree of enhanced binding are consistent with simple electrostatic theory. Moreover, when both Asp changes were introduced together, the binding affinity for Ca/sup 2 +/ was found to be increased about 6-fold over that for the wild-type protein, suggesting an independent and nearly additive effect on the total electrostatic potential at this locus.« less

Regeneration patterns in old-growth Abies-Betula forests in the Wolong Natural Reserve, Sichuan, China

Abstract: (1) Regeneration patterns of Abiesfaxoniana, Betula utilis and B. albosinensis in central Sichuan, China were interpreted by stand structural analysis (age, size, horizontal patterning) of tree populations in old-growth ( > 250 years) stands. (2) Seedlings, saplings and young trees were scarce in stands where bamboo (Sinarundinaria fangiana) impeded tree regeneration. Shrub density and woody plant species richness were lower in stands with high bamboo cover. (3) Regeneration patterns indicate that A. faxoniana and B. utilis relative densities were similar where bamboo was dense and that A. faxoniana was more than twice as abundant as B. utilis where bamboo cover was low or absent. Bamboos seem to impede A.faxoniana regeneration more than that of B. utilis. Both species regenerated in canopy gaps, but A. faxoniana less so than B. utilis where bamboos were dense. This produces higher Betula density in bamboo stands. Sizes of young patches of B. utilis tended to be larger than patches of A.faxoniana. Partitioning of gaps by size may contribute to coexistence of A. faxoniana and B. utilis in old-growth stands.

The visual pigments of crabs. I: Spectral characteristics

Abstract: 1. The visual pigments of 27 species of crabs from a variety of habitats were investigated by microspectrophotometry of the isolated rhabdomeric photoreceptors. The rhodopsins ranged inλmax from 473 to 515 nm (Tables 1 and 2). No evidence was found for the presence of more than a single rhodopsin in retinular cells 1–7. 2. All rhodopsins produced thermally stable metarhodopsins on irradiation with long-wavelength light. The metarhodopsins of hermit crabs (Anomura: section Paguridea) all absorbed hypsochromically to their rhodopsins. Brachyuran metarhodopsins. with the exception of that ofCancer irroratus, absorbed at the same spectral position as the rhodopsin or bathochromically to it. 3. The absorption spectra of all rhodopsins but one could be fit closely by the Dartnall nomogram. Since prior studies have located only retinal in the eyes of crabs, retinal may serve universally as a chromophore in crab visual pigments

How violent are fast controls?, II

Abstract: For any controllable, linear system it is clear that the minimum control energy must increase unboundedly as the available time for exact control decreases to 0. This is made precise, obtaining asymptoticallyO(T −(K+1/2) behavior for the norm of the control operator whereK is the order of the “least controllable” modes (the minimal exponent for the rank condition).

Vocal congruence in mother-infant play.

Abstract: Turn-taking is the fundamental temporal structure of adult dialogue. This structure defines two types of joint silence: intrapersonal pause (silence bounded by the vocalizations of a single speaker) and switching pause (silence bounded by the vocalizations of different speakers). Switching pauses mark the boundaries of the turn exchange. In adult conversation the mean durations of both types of pause are characteristically matched between partners. This matching, termed “vocal congruence,” occurs developmentally earlier in the case of switching pauses. We hypothesized and confirmed that mothers and infants match switching pauses but not intrapersonal pauses at 4 months, even though the infants' vocalizations are prelinguistic. Second, since there are known affective correlates of vocal congruence in adult conversation, we hypothesized a similar affective correlate for mother-infant vocal congruence. We found, for the intrapersonal pause only, that the degree of matching within a dyad correlated with infant affective engagement. We conclude, from switching pause congruence, that a turntaking dialogic structure is being regulated in the mother-infant pair at 4 months in the same way as seen in adult conversation. Thus, both the temporal structure of adult dialogue and its affective correlate are prelinguistic.

Optimization of efficiency in the glyoxalase pathway.

Abstract: A quantitative kinetic model for the glutathione-dependent conversion of methylglyoxal to D-lactate in mammalian erythrocytes has been formulated, on the basis of the measured or calculated rate and equilibrium constants associated with (a) the hydration of methylglyoxal, (b) the specific base catalyzed formation of glutathione-(R,S)-methylglyoxal thiohemiacetals, (c) the glyoxalase I catalyzed conversion of the diastereotopic thiohemiacetals to (S)-D-lactoylglutathione, and (d) the glyoxalase II catalyzed hydrolysis of (S)-D-lactoylglutathione to form D-lactate and glutathione. The model exhibits the following properties under conditions where substrate concentrations are small in comparison to the Km values for the glyoxalase enzymes: The overall rate of conversion of methylglyoxal to D-lactate is primarily limited by the rate of formation of the diastereotopic thiohemiacetals. The hydration of methylglyoxal is kinetically unimportant, since the apparent rate constant for hydration is (approximately 500-10(3))-fold smaller than that for formation of the thiohemiacetals. The rate of conversion of methylglyoxal to (S)-D-lactoylglutathione is near optimal, on the basis that the apparent rate constant for the glyoxalase I reaction (kcatEt/Km congruent to 4-20 s-1 for pig, rat, and human erythrocytes) is roughly equal to the apparent rate constant for decomposition of the thiohemiacetals to form glutathione and methylglyoxal [k(obsd) = 11 s-1, pH 7]. The capacity of glyoxalase I to use both diastereotopic thiohemiacetals, versus only one of the diastereomers, as substrates represents a 3- to 6-fold advantage in the steady-state rate of conversion of the diastereomers to (S)-D-lactoylglutathione.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid sequence of bovine cardiac troponin I.

Abstract: Troponin I (TnI) is the inhibitory subunit of troponin, the thin filament regulatory complex which confers calcium sensitivity to striated muscle actomyosin ATPase activity. We have determined the amino acid sequence of TnI from adult bovine cardiac muscle. This protein is a single polypeptide chain of 211 amino acids with an acetylated amino terminus, a calculated molecular weight of 23,975, and a net charge of +17 at neutral pH. There was no evidence for heterogeneity of the sequence. Comparison with other available TnI sequences shows an amino-terminal extension of 27-33 residues which is present in cardiac but not skeletal TnI. The remainder of the polypeptide is common to both cardiac and skeletal TnI. In the amino-terminal half of the common polypeptide, only 29% of the residues are invariant in all sequences. The carboxyl-terminal half (residues 124-210) is much more highly conserved, with 66% invariant residues. Bovine cardiac TnI and rabbit cardiac TnI are very similar in sequence: only 12 of 26 residues are identical in the amino-terminal segments, but the remaining residues of the proteins are 97% identical.

Organization of microtubules in centrosome-free cytoplasm.

Abstract: Many different cell types possess microtubule patterns which appear to be polarized and oriented, in part, by cytoplasmic factors not directly associated with a centrosome Recently, we demonstrated that cytoplasmic extensions ("arms") of teleost melanophores will reorganize their microtubule population outward from their centers after surgical isolation (McNiven, M A, M Wang, and K R Porter 1984 Cell 37:753-765) In the study reported here, we examine microtubule dynamics within the centrosome-free fragments and find that, after severing, microtubule reorganization is initiated at the proximal (cut) end of an arm and migrates distally with the aggregated pigment mass until it becomes permanently positioned at the middle of the arm Computer-aided image analysis demonstrates that this middle position is located at the arm centroid, implicating the action of a cytoplasmic gel in this process Morphological studies of arms devoid of pigment reveal that microtubules do not emanate from a single site or structure within the centroid area, but from a more generalized region Taken together, these findings suggest that factors distributed throughout cytoplasm participate in microtubule assembly and organization

In situ adsorption for enhanced alkaloid production by Catharanthus roseus

Abstract: A significant fraction (10–40%) of the indole alkaloids produced byCatharanthus roseus was observed to be secreted into the medium. When a neutral polymeric resin, known to adsorb these alkaloids, was added to the cultivation medium, the accumulation of total indole alkaloids and the specific alkaloids, ajmalicine and serpentine were stimulated. Sorbent addition was also observed to result in increased ratios of ajmalicine to serpentine, which suggests the potential of using in situ adsorption to direct metabolism toward a specific product or intermediate within a given pathway.

Reinforcement schedules: Retroactive and proactive effects of reinforcers inserted into fixed-interval performances.

Abstract: The responding maintained by a reinforcer depends on the relation of the reinforcer not merely to the response that produces it but also to other preceding responses. Early responses in a sequence that ends in a reinforcing consequence make smaller contributions to later response rates than more recent ones, by virtue of the longer delays that separate them from the reinforcer. This study shows that the relation between a response and a later reinforcer contributes to responding only if no other reinforcers intervene; in other words, each reinforcer blocks responses that precede it from the effects of later reinforcers. Pigeons' pecks were maintained by fixed-interval (FI) schedules of food reinforcement. When FI 60-s (short) and FI 75-s (long) schedules began simultaneously within constant 150-s cycles, long FIs did not affect short-FI performances, but short FIs eliminated the first 60 s of long-FI performances. Removing either short-FI reinforcers or short-FI stimuli showed that short-FI reinforcers and not short-FI stimuli blocked the first 60 s of the long-FI performance from the retroactive effects of the long-FI reinforcer. With FI 15-s and FI 75-s schedules, the short-FI reinforcer was followed by reduced long-FI responding, but a schedule that prevented discrimination based on time since a reinforcer eliminated this proactive effect of the short-FI reinforcer. In other words, the retroactive effects were reinforcer effects whereas the proactive effects were discriminative effects. Quantitative descriptions of variable-interval performances, in which reinforcer effects may operate in the absence of temporal discriminative effects, can be derived from these relations.

Chronic clorgyline treatment of Syrian hamsters: an analysis of effects on the circadian pacemaker.

Abstract: Clorgyline, a type A monoamine oxidase inhibitor with antidepressant properties when administered to depressed patients, is often associated with disturbances of the human sleep-wake cycle. In order to assess its effects on the mammalian circadian system, this drug was administered chronically to Syrian hamsters. It was found to affect the hamster circadian system in four specific ways. Clorgyline increased the intrinsic period of wheel-running ac tivity, altered the phase response curve to brief light pulses, altered the educed waveform of running activity in animals maintained in light-dark cycles or constant darkness, and in creased the activity-rest ratio in animals maintained in constant darkness. Our data support the interpretation that clorgyline exhibits direct or indirect input to the circadian pacemaker and alters the processing of photic information to the pacemaker.

Heat and Violence: New Findings from Dallas Field Data, 1980-1981

Abstract: Research in both laboratory and field settings has suggested a link between thermal stress and violent behavior, and both linear and curvilinear models have been investigated. A dearth of field studies prompted the analysis reported here, which is based on data for some 10,000 aggravated assaults occurring the City of Dallas in 1980 (a summer of severe heat stress) and 1981. This analysis replicates and extends certain aspects of recent work by Anderson and Anderson (1984) relating to the so-called linear and curvilinear hypotheses. Thermal stress is measured in two ways: a Discomfort Index (DI), which takes into account the influence of humidity acting in concert with temperature, and ambient temperature. Regression analyses were performed in two stages. In the first, data for all neighborhoods and all days of the study period were combined into ambient temperature and DI models. At the second stage, models differentiated between the three levels of neighborhood socioeconomic status. With weekend controlled, DI and ambient temperature were significant independent variables in the 'overall' model and in medium and low status neighborhoods. However, when linear effects were controlled, the curvilinear measures were never significant. The analysis generally tended to confirm Anderson and Anderson's suggestion that a reduction of aggression with increasing temperature does not appear to occur within the normal range of temperatures. This analysis further suggested that the hypothesized curvilinear effect is weak, if not entirely absent, even during conditions of extreme heat.

Physical Abuse of Children

Abstract: Cruelty toward and maltreatment of children has become a topic of much social concern during the past 20 years. The purpose of this chapter is to summarize the roots of this concern, analyze the magnitude of the problem, review current knowledge and, lastly, provide a framework for considering treatment, prediction, and prevention. Only physical abuse will be discussed; other forms of maltreatment such as sexual abuse, neglect, and institutional abuse are beyond the scope of this review. The terms abuse and maltreatment will be used synonymously and refer to inflicted trauma or injury by parents or other caregivers.

Calcium regulation of pigment transport in vitro.

Abstract: Calcium has been implicated in the regulation of many cellular motility events. In this study we have examined the role of different Ca2+ concentrations on the in vitro transport of pigment within cultured chromatophores. Cells treated with Brij detergent for 1-2 min were stripped of their plasma membranes, leaving their cytoskeleton and associated pigment granules exposed to the external milieu. We found that retrograde pigment transport (aggregation) is induced upon addition of 1 mM MgATP2- with 10(-7) M free Ca2+, while an orthograde transport (redispersal) of pigment results from lowering the concentration of free Ca2+ to 10(-8) M while maintaining 1 mM MgATP2-. These Ca2+-regulated movements are ATP dependent but are apparently independent of cAMP and insensitive to calmodulin inhibitors. The observations reported here provide novel evidence that the concentration of free Ca2+ acts to regulate the direction of intracellular organelle transport.

Crossing over in males of higher diptera (Brachycera)

Abstract: Achiasmatic meiosis, or meiosis without crossing over, is characteristic of all higher Diptera males (suborder Brachycera). However, several cases of spontaneous crossing over in males have been reported in several different species. An examination of the published data suggests that recombinant chromosomes recovered from heterozygous males are usually the result of spontaneous crossing over in premeiotic cells. Mitotic, or somatic, crossing over probably occurs at a low frequency in all Diptera. When the crossover occurs in a gonial cell line, the recombinant chromosomes can be recovered in the gametes as presumptive meiotic crossovers. In cases where there is a translocation between the Y chromosome and an autosome, the segregation of the chromosomes from the translocation complex can produce aneuploids that phenotypically appear to be crossovers. Chromosome rearrangements and insertion elements, including the male sex-determining factor in Musca domestica and Megaselia scalaris, increase the frequency of exchange. Drosophlia ananassae appears to be an exception to the above. Genetic evidence in D. ananassae suggests that crossing over is a meiotic event and is controlled by a series of suppressors and enhancers.

Chloramphenicol induction of cat-86 requires ribosome stalling at a specific site in the leader.

Abstract: The plasmid gene cat-86 specifies chloramphenicol-inducible chloramphenicol acetyltransferase in Bacillus subtilis. Induction by the antibiotic is primarily due to activation of the translation of cat-86-encoded mRNA. It has been suggested that the inducer stalls ribosomes at a discrete location in the leader region of cat-86 mRNA, which causes the destabilization of a downstream RNA secondary structure that normally sequesters the cat-86 ribosome binding site. It is the destabilization of this RNA secondary structure that permits translation of the cat-86 coding sequence. In the present report, we show that ribosomes that were stalled in the cat-86 leader by starvation of host cells for the amino acid specified by leader codon 6 induced gene expression to a level above that detected when cells were starved for the amino acids specified by leader codons 7 and 8. Starvation for amino acids specified by leader codons 3, 4, or 5 failed to activate cat-86 expression. These results indicate that the stalled ribosome that is most active in cat-86 induction has its aminoacyl site occupied by leader codon 6. To determine if chloramphenicol also stalled ribosomes in the cat-86 regulatory leader such that the aminoacyl site was occupied by codon 6, we separately changed leader codons 3, 4, 5, and 6 to the translation termination (ochre) codon TAA. Each of the mutated genes was tested for its ability to be induced by chloramphenicol. The results show that replacement of leader codons 3, 4, or 5 by the ochre codon blocked induction, whereas replacement of leader codon 6 by the ochre codon permitted induction. Collectively, these observations lead to the conclusion that cat-86 induction requires ribosome stalling in leader mRNA, and they identify leader codon 6 as the codon most likely to be occupied by the aminoacyl site of a stalled ribosome that is active in the induction.

H-2Kb antigen expression has no effect on natural killer susceptibility and tumorigenicity of a murine hepatoma.

Abstract: Recent reports suggested a correlation between decreased expression of tumor cell MHC class I Ag and increased susceptibility to NK cells These studies led to the hypothesis that tumor cells displaying reduced levels of MHC class I Ag have reduced tumorigenicity in vivo because they are eliminated from the host by endogenous NK cells The present studies use the murine hepatoma BW7756 and a spontaneous H-2Kb loss variant, Hepa-1, to test this hypothesis The parental BW7756 tumor is highly malignant in syngeneic C57L/J hosts while Hepa-1 cells do not give rise to tumors, suggesting that the loss of H-2Kb Ag expression correlates with decreased tumorigenicity and NK susceptibility Hepa-1 cells were therefore transfected with an H-2Kb gene to generate H-2Kb Ag expressing clones The resulting clones were tested for tumorigenicity Syngeneic or NK-deficient C57BL/6-beige/beige mice challenged with Hepa-1 or the H-2Kb transfectants rejected the cells, suggesting that reexpression of H-2Kb Ag does not restore tumorigenicity and that NK cells are not involved in Hepa-1 rejection In vitro H-2Kb Ag-negative and -positive Hepa-1 cells are equally susceptible to tilorone-boosted NK cells, indicating that MHC class I Ag expression also does not affect in vitro NK susceptibility Tumor challenged athymic nude and sublethally irradiated syngeneic mice develop tumors demonstrating that T cells are probably responsible for rejection of the Hepa-1 tumor, and that H-2Kb Ag expression has no effect on rejection Inasmuch as the expression of H-2Kb Ag on Hepa-1 cells does not effect tumorigenicity or in vitro NK susceptibility, the previously reported association between reduced MHC class I Ag levels and increased NK susceptibility is not universally applicable

Centripetal forces in spatial voting: On the size of the Yolk

Abstract: The yolk, the smallest circle which intersects all median lines, has been shown to be an important tool in understanding the nature of majority voting in a spatial voting context. The center of the yolk is a natural ‘center’ of the set of voter ideal points. The radius of the yolk can be used to provide bounds on the size of the feasible set of outcomes of sophisticated voting under standard amendment procedure, and on the limits of agenda manipulation and cycling when voting is sincere. We show that under many plausible conditions the yolk can be expected to be small. Thus, majority rule processes in spatial voting games will be far better behaved than has commonly been supposed, and the possible outcomes of agenda manipulations will be generally constrained. This result was first conjectured by Tullock (1967).

Nalbuphine analgesia in the prehospital setting

Abstract: Forty-six patients with moderate to severe pain caused by orthopedic injuries, burns, multiple trauma, or intraabdominal conditions were treated with intravenous (IV) nalbuphine hydrochloride (Nubain; DuPont Pharmaceuticals, Wilmington, DE) by paramedics before arrival at the hospital. Patients who weighed less than 60 kg received 15 mg nalbuphine, and patients weighing greater than 60 kg received 20 mg nalbuphine. Forty-one of 46 patients (89%) experienced pain relief from nalbuphine, with maximum relief occurring within 15 minutes after the administration of the drug. Two addicted patients received no pain relief. There were no untoward side effects following nalbuphine administration, and the patients' heart rates, mean arterial pressures, and respiratory rates remained constant and stable throughout the study period. Repeated assessment of the patient by paramedics in the field was not impaired by nalbuphine treatment. In summary, nalbuphine hydrochloride is a useful and safe analgesic drug for IV use by paramedics in the prehospital setting.

Tree replacement patterns in subalpine Abies-Betula forests, Wolong Natural Reserve, China

Abstract: Vegetation in canopy gaps of two old-growth Abies-Betula forest stands, one with bamboo the other without, was measured. The structure of gap vegetation at each site was used to derive tree replacement probabilities. Transition probabilities indicate different tree replacement trends in forests with bamboo compared to those without. Projected compositions show Betula to be the most abundant species in bamboo stands while Abies remains most abundant where bamboo was absent. A dense bamboo sward seems to reduce the probability of Abies filling gaps by inhibiting establishment and growth of seedlings. Bamboo preempts space after canopy gap formation by increasing shoot production which reduces opportunities for establishment and growth of other woody species. Differences in dispersal ability and longevity of Abies and Betula appear to be important factors contributing to their coexistence forests with a small canopy gap disturbance regime.

Diffusion-dependent rates for the hydrolysis reaction catalyzed by glyoxalase II from rat erythrocytes.

Abstract: Glyoxalase II from rat erythrocytes is a near optimal catalyst for the hydrolysis of S-D-lactoylglutathione in the sense that the magnitude of kcat/Km is limited, in large part, by the rate constant for diffusion-controlled encounter between substrate and active site. The experimental basis for this conclusion is derived from the dependencies of the kinetic properties of the enzyme on solution viscosity (pH 7, Ic = 0.1 M, 25 degrees C). When sucrose is used as a viscogenic agent, kcat/Km for S-D-lactoylglutathione (8.8 x 10(5) M-1 s-1) decreases markedly with increasing solution viscosity. This effect appears not to be due to a sucrose-induced change in the intrinsic kinetic properties of the enzyme, since kcat/Km for the slow substrate S-acetylglutathione (3.7 x 10(4) M-1 s-1) is nearly independent of solution viscosity. Quantitative treatment of the data using Stoke's law indicates that the rate of hydrolysis of S-D-lactoylglutathione will be approximately 50% diffusion limited when [substrate] much less than Km; the encounter complex between enzyme and substrate partitions nearly equally between product formation and dissociation to form free enzyme and substrate. The same conclusion is reached when glycerol is used as a viscogenic agent, once the apparent activation effect of glycerol on the intrinsic activity of the enzyme is taken into account. Finally, the rate of formation of the encounter complex between substrate and active site may be governed to a significant extent by charge-charge interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of line mixing on atmospheric brightness temperatures near 15 μm

Abstract: The effect of line mixing on the effective blackbody brightness temperature of the earth in the region of the 15-micron nu 2 Q branch of CO2 is calculated. The procedures used to compute line mixing follow those used to successfully model mixing observed in laboratory spectra of two near-infrared CO2 Q branches. The atmospheric radiances are calculated between 664 and 670/cm, a spectral region that is of interest for sounding the upper troposphere and the stratosphere. Mixing was found to lower the observed brightness temperatures by as much as 3 K for some temperature profiles. Ignoring this effect would significantly impact the ability of advanced sounders to produce temperature retrievals which meet the projected accuracy requirement of 1 K/km.