Showing papers by "Utrecht University published in 1980"

The mathematical theory of L systems

Abstract: The paper gives a survey of the different areas of the theory of developmental systems and languages. It is organized in such a way that it discusses typical results obtained in each particular problem area. The results quoted may not always be the most important ones but they are quite representative for the direction of research in this theory. Proofs are not given and, consequently, the basic techniques for solving problems in this theory are not discussed. An attempt has been made to cover also the most recent results. Most of the results have not yet appeared in print. To appear in J. Tou (ed. ), Advances in Information Systems Science, Plenum Press.

The scope of metastable peak observations

Abstract: This short review focuses attention upon the present status of metastable ion studies with emphasis upon the relationship between metastable peak shapes, ion structur and fragmentation mechanisms. Some recommendations are made concerning nomenclature and the reporting of observations on Gaussian-type metastable peaks. Experimental methods for recording relative abundances of metastable peaks are critically appraised. The relationship between metastable ion phenomena and isomerization of gaseous ions is reviewed with particular attention drawn to the effect of rate-determining isomerizations. The shapes of Gaussian-type metastable peaks are discussed in some detail and selected examples from recent studies are used to show that such peaks may, by appropriate experiments, be separated into two Gaussian-type components thus revealing new features of the fragmentation reaction. The magnitude and significance of released kinetic energies, T, are considered and it is stated that few conclusions can be drawn from the evaluation of T alone; the importance of accurate thermochemical data as an aid to understanding and interpreting kinetic energy release data is emphasized. Other topics discussed include composite metastable peaks, metastable peaks produced in chemical ionization and field ionization and the partitioning of internal energy of the fragmenting ion into translational degrees of freedom of the products, for reactions with and without a reverse energy barrier.

Purification and some characteristics of an ACTH sensitive protein kinase and its substrate protein in rat brain membranes

Abstract: ACTH inhibits the phosphorylation of a rat brain membrane-bound protein (B-50). Both the protein kinase and the substrate protein could be extracted from the membranes by means of treatment with Triton X-100 in 75 mM-KCl. Using column chromatography over DEAE-cellulose and ammonium sulphate precipitation a protein fraction (ASP 55–80) enriched in endogenous B-50 phosphorylating activity was obtained. The time course of the endogenous phosphorylation of B-50 in this fraction showed a linear incorporation with time for at least 10 min and reached an estimated maximal incorporation of 0.65 mol P/mol B-50 after 60 min. The inhibition by ACTH1_24 of the B-50 protein kinase in ASP 55–80 was dose-dependent; the half-maximal effective concentration was 5 × 10−6 M, being 10 to 50 times lower as compared with intact synaptic plasma membranes (SPM). cAMP, cGMP and various endor-phins had no effect on the B-50 protein kinase. The B-50 protein kinase required both magnesium and calcium for optimal activity. Using two-dimensional electrophoresis on polyacrylamide slab gels the B-50 protein kinase and the B-50 protein could be identified and purified. The isoelectric point (IEP) of the kinase is 5.5 and the apparent molecular weight 70,000, whereas the IEP of the substrate protein B-50 is 4.5 and the apparent molecular weight 48,000. Amino acid analysis on microgram quantities of purified kinase and B-50 protein revealed basic/acidic amino acid ratios in agreement with the respective lEP's. It is speculated that the inhibition of B-50 protein kinase may be related to known modulatory effects of ACTH and related peptides on certain types of neurotransmission and behaviour.

Modulation of brain polyphosphoinositide metabolism by ACTH-sensitive protein phosphorylation.

Abstract: Phosphorylation of membrane components is thought to be an important process in membrane function1. Phosphorylated proteins2 and a special class of phospholipids, the (poly)phos-phoinositides (poly PI)3, are implicated in the regulation of membrane permeability and synaptic transmission in neurones. For many years, protein phosphorylation and poly PI metabolism have been studied in parallel without knowledge of their possible interaction. We report here that the ACTH-sensitive protein kinase/B-50 protein complex which we recently isolated in soluble form from rat brain synaptosomal plasma membranes4,5 has lipid phosphorylating activity. Exogenously added phosphatidylinositol 4-phosphate (DPI) is phosphorylated to phosphatidylinositol 4,5-diphosphate (TPI), and this DPI-kinase activity is dependent on the state of phosphorylation of the protein kinase/B-50 protein complex. The results imply that phosphorylation of protein may affect the metabolism of (poly)PI in brain cell membranes.

Model experiments on the 100 000 yr glacial cycle

Abstract: It is believed that during the Quaternary era changes in global ice volume were mainly due to changes in the size of the ice sheets on the Eurasian and American continents. Time spectra of oxygen isotope records from deep-sea cores and of the Earth's orbital parameters are remarkably similar in the 10,000–120,000-yr range1,2, suggesting that changes in global ice volume are forced by insolation variations. Model studies by Weertman3,4 and Pollard5 have confirmed this point to some extent: the 20,000- and 40,000-yr cycles can be reproduced, but the 100,000-yr cycle does not show up. Recently, Imbrie and Imbrie6 have fitted simple nonlinear mathematical models to δ18O curves. They found that reasonable fits are obtained if the time scale for ice-sheet growth is about 27,000 yr and for decay about 7,000 yr. The present study considers the problem of the 100,000-yr cycle in a similar way. Experiments with a Northern Hemisphere ice-sheet model show that the 100,000-yr cycle and its sawtooth shape may be explained by ice sheet/bedrock dynamics alone. This cycle seems to be an internally generated feature and is not forced by variations in the eccentricity of the Earth's orbit.

Physiological and biochemical aspects of the valve snap and valve closure responses in the giant scallopPlacopecten magellanicus

Abstract: 1. The giant scallopPlacopecten magellanicus responds to stimulation with starfish extract by snapping the valves in a series of rapid adductions. After approximately 25–35 adductions, the scallop does not respond to further stimulation, and usually closes the valves. 2. Snapping of the valves results in an accelerated heart rate, increased stroke volume and enhanced cardiac output. The supply of oxygen to the adductor muscle will be increased but must be insufficient, as blood\(P_{{\text{O}}_{\text{2}} }\) decreases to 15 mm Hg and energy-producing anaerobic pathways are invoked (de Zwaan et al., 1980). There is an increase in the total carbon dioxide content of the blood and a fall in blood pH. When the scallop reopens, there is a transient increase in oxygen uptake. 3. The restoration of physiological functions to normal values takes several hours. 4. During valve closure, the\(P_{{\text{O}}_{\text{2}} }\) of the mantle water decreases from 145 mm Hg to 80 mm Hg, blood\(P_{{\text{O}}_{\text{2}} }\) from 85 mm Hg to 40 mm Hg. This is sufficient to maintain a degree of aerobic metabolism, and oxygen uptake continues. There is no change in heart rate, but blood pH decreases gradually.

D-2-hydroxyglutaric aciduria: case report and biochemical studies.

Abstract: A patient with protein-losing gastroenteropathy and egg allergy has been shown to have a previously unrecognized organic aciduria,d-2-hydroxyglutaric aciduria. The observations made are consistent with an inherited metabolic disorder in the catabolism of 5-aminolaevulinate possibly due to deficient activity of a specificd-2-hydroxyglutarate dehydrogenase.

Genetic and environmental variation in clutch size of the great tit (Parus major)

Abstract: An analysis is made of genetic and non-genetic components in the number of eggs in the completed first clutch of the Great Tit. 1) It is doubtful whether a causal relation between density and clutch size exists. 2) There is hardly a systematic effect of age on clutch size. 3) There is an annual variation in clutch size with similar changes in individual females in the same population, but it is hardly correlated between populations. This emphasizes a lack of genotype-environment interaction. 4) Within populations there is no detectable variation in clutch size that can be attributed to differences in habitat quality. 5) About 40% of the total phenotypic variation in clutch size is genetic variation. Several ways of eliminating a possible resemblance through correlated environments yield the same result. 6) Selection for clutch size is demonstrated in several years. 7) The implications for rapid evolutionary change in mean clutch size are discussed.

Selective conversion of β-endorphin into peptides related to γ- and α-endorphin

Abstract: β-Endorphin (β-LPH61–91) is a well known endogenous opioid ligand. It and related peptides have recently been implicated in the control of adaptive behaviour. Smaller β-endorphin fragments appeared to be more active moieties than the parent molecule in a number of behavioural situations1. Their effects seemed to occur independently of interaction with opiate receptor sites in the brain. Moreover, elimination of the opiate-like properties of γ-endorphin (β-LPH61–77) by removing the N-terminal amino acid yielded des-tyrosine-γ-endorphin (β-LPH62–77, dTγE) which had greater behavioural activity than γ-endorphin2,3. The CNS effects of dTγE resembled those of neuroleptic drugs in several test systems, α-Endorphin (β-LPH61–76) exerted effects opposite to those of dTγE and in some aspects its activity was comparable to that of psychostimulant drugs4. This opposition of effects suggests that a balance between γ- and α-type endorphins is involved in the control of brain function5. We report here that either γ-endorphin and dTγE or α-endorphin and des-tyrosine-α-endorphin (β-LPH62–769 dTαE) can be formed preferentially from β-endorphin by enzymes associated with an enriched synaptosomal plasma membrane fraction from brain. It is suggested that these enzymes have a role in brain homeostatic mechanisms by regulating the generation of these substances.

Circadian rhythmicity of the activity of hydroxyindole-O-methyl transferase (HIOMT) in the formation of melatonin and 5-methoxytryptophol in the pineal, retina, and harderian gland of the golden hamster.

Abstract: The day and night rhythms in the activity of HIOMT in the formation of melatonin and of 5-methoxytryptophol have been determined in the pineal, retina and Harderian gland of the adult male golden hamster. In all hamsters used there was no detectable HIOMT activity in the deep pineal. In the superficial pineal HIOMT activity, involved in the synthesis of melatonin (Mel), was observed to be high at the end of the dark period and at the middle of the light period. Considering the HIOMT activity involved in the production of 5-methoxytryptophol (5-MTL), an increase in 5-MTL synthesis was observed only during the light period. Comparing the peak of Mel-production with that of 5-MTL it appears that during the light period the pineal produces more 5-MTL than Mel. In the Harderian glands, the circadian course of HIOMT activity involved in the synthesis of Mel seems to run parallel to that of the enzyme implicated in 5-MTL synthesis, both being stimulated at the end of the dark period. The activity of HIOMT in 5-MTL production is, however, always approximately 2 times higher than for Mel synthesis. In the retina the synthesis of Mel and 5-MTL is not significantly higher during the dark period than during the light period. However, the production of 5-MTL is larger than that of Mel. It appears that (1) with the exception of the end of the dark period, the extra-pineal synthesis of Mel and 5-MTL is always higher than that in the pineal; (2) the circadian synthesis of 5-methoxyindoles is different in each organ, and (3) in the pineal the circadian activity of HIOMT involved in 5-MTL formation is different from that of the same enzyme involved in the formation of Mel. The results are discussed.

Qualitative and quantitative freeze-fracture studies on olfactory and nasal respiratory structures of frog, ox, rat, and dog. I. A general survey.

Abstract: A comparative study using freeze-fracturing has been made of surface structures of olfactory and nasal respiratory epithelia of frog, ox, rat and dog. Special attention has been paid to cilia and microvilli present at these surfaces, although the observations include various other structures such as small intracellular vacuoles present in the olfactory receptor endings and infrequent brush cells. Within the mucus overlying the olfactory epithelium membranous vesicles, often attached to olfactory cilia, are seen. Some of these show intramembranous particle distributions similar to those of the rest of the cilia, whereas others are devoid of particles. Smooth vesicles are also found in the mucus of other types of epithelium (respiratory epithelium and Bowman's glands). The freeze-fracture morphology of intracellular secretory vacuoles present in olfactory supporting, Bowman's and respiratory glandular cells of the frog is similar in all these epithelia. Quantitative comparisons are made of the different structures of interest. When corrected for cilia which were not observed, mammalian receptor endings bear 17 cilia on average, whereas frog receptor endings have 6 cilia. The relative magnitudes of the diameters of the cilia and microvilli are, except for frog, the same for all species studied. Dimensions of other structures e.g., axons, dendrites and dendritic endings are compared in the various species. Freeze-fracture diameters are usually larger than those seen by techniques using dehydration. Dendritic ending densities range from 4.5 × 106 (frog) to 8.3 × 106 (dog) endings per cm2. Possible sex-dependent differences are only found for these densities and dendritic ending diameters.

Association of lysophosphatidylcholine with fatty acids in aqueous phase to form bilayers.

Abstract: Lysophospholipids have been implicated in a variety of physiological processes1. In vivo lysophospholipids are invariably produced with fatty acids as the product of hydrolysis by phospholipase A2 (ref. 2). Therefore, it is of considerable interest to examine the properties of the mixture of these lipids in aqueous suspensions. Results presented here demonstrate that a mixture of fatty acid and lysophosphatidylcholine forms a bilayer type of organisation even though the individual components form micelles when dispersed in an aqueous phase.