Showing papers on "Substrate (chemistry) published in 1980"
TL;DR: From the kinetic data, it becomes evident that the reductive amination reaction is highly adaptive to the ammonium environment.
14,480 citations
TL;DR: Strains of Trichoderma, particularly T. reesei and its mutants, are good sources of extracellular cellulase suitable for practical saccharification and carbon compounds derived from enzymatic hydrolysis of cellulose will be used as fermentation and chemical feedstocks as soon as the process economics are favourable.
568 citations
TL;DR: The model, developed for steady-state-biofilm kinetics with a single substrate, couples the flux of substrate into a biofilm to the mass (or thickness) of biofilm that would exist at steady- state for a given bulk substrate concentration.
Abstract: A steady-state biofilm is defined as one that has neither net growth nor decay over time. The model, developed for steady-state-biofilm kinetics with a single substrate, couples the flux of substrate into a biofilm to the mass (or thickness) of biofilm that would exist at steady-state for a given bulk substrate concentration. Based on kinetic and energetic constraints, this model predicts for a single substrate that a steady-state bulk concentration, Smin, exists below which a steady-state biofilm cannot exist. Thus, in the absence of adsorption of bacteria from the bulk water and for substrate concentration below Smin, substrate flux and biofilm thickness are zero. Equations are provided for calculating the steady-state substrate flux and biofilm thickness for S greater than Smin. An example is provided to demonstrate the use of the steadystate model.
457 citations
TL;DR: Benzyloxycarbonyl-phenylalanyl-arginine 4-methyl-7-coumarylamide was found to be an excellent substrate for the fluorimetric assay of cathepsin B, and arginine 4,methyl- 7-cOUmarylamides for cathepsypsin H.
Abstract: Benzyloxycarbonyl-phenylalanyl-arginine 4-methyl-7-coumarylamide was found to be an excellent substrate for the fluorimetric assay of cathepsin B, and arginine 4-methyl-7-coumarylamide for cathepsin H. Procedures were developed that are very convenient, and avoid the hazards associated with the use of naphthylamides.
383 citations
233 citations
TL;DR: The autoactivation described herein may provide a sufficient initial concentration of activated HF to initiate the intrinsic coagulation, fibrinolytic, and kinin-forming cascade in a manner consistent with autoactivation.
225 citations
TL;DR: The model of steady‐state‐biofilm kinetics successfully predicted substrate utilization and biofilm thickness without the need for fitting factors and implies that organic materials may persist in water and wastewater because they are too low in concentration to supply sufficient energy to sustain the microorganisms.
Abstract: Laboratory-scale biofilm reactors were used to evaluate a model of the kinetics of steady-state biofilm and the concept that there is a minimum concentration, Smin, below which no steady-state activity can occur. With acetate as the ratelimiting substrate, the steady-state concept of Smin was verified for naturally grown biofilms. Substrate removal and biofilm thickness declined rapidly as the substrate concentration approached Smin, which was 0.66 mg/liter for acetate. Using independently derived kinetic parameters, the model of steady-state-biofilm kinetics successfully predicted substrate utilization and biofilm thickness without the need for fitting factors. The results imply that organic materials may persist in water and wastewater, in part, because they are too low in concentration to supply sufficient energy to sustain the microorganisms.
224 citations
TL;DR: Inhibition by the pentaglutamate derivative offers a means by which folylpolyglutamates could regulate their own synthesis and indicate that the predominant chain length of folates in rat liver may be determined solely by the substrate specificity of the rat liver synthetase.
210 citations
TL;DR: This chapter reviews that large number of cellular enzymes are located in membranes and the growing interest in the mechanisms, controlling their activities, has incited a number of biochemists to study in detail certain aspects of heterogeneous catalysis.
Abstract: Publisher Summary This chapter reviews that large number of cellular enzymes are located in membranes and the growing interest in the mechanisms, controlling their activities, has incited a number of biochemists to study in detail certain aspects of heterogeneous catalysis. Because of the difficulties encountered in the purification of these membrane proteins, the knowledge of their kinetic behavior is still very scanty. This explains the reason most experimental approaches used so far deal with model systems based on the combination either of (a) an immobilized enzyme + soluble substrate or (b) a soluble enzyme + insoluble substrate. The naturally occurring (phospho) lipids are important building stones of the biological membranes. They are water insoluble and spontaneously form molecular aggregates, such as monomolecular films, bi-layers, emulsions, liposomes, or micelles. A number of soluble enzymes play an important role in such biological events as digestion, lipid transport, and lipid metabolism are known and have been isolated. It discusses that phospholipases are used in the determination of asymmetric phospholipid distribution in membranes. The substrate that forms molecular aggregates makes lipolysis a very attractive system for the studies of interfacial enzyme kinetics.
207 citations
TL;DR: A new one-step method for the light and electron microscopic localization of the ouabain-sensitive, K-dependent p-nitrophenylphosphatase (K-NPPase) activity of the Na-K-ATPase complex is introduced.
Abstract: A new one-step method for the light and electron microscopic localization of the ouabain-sensitive, K-dependent p-nitrophenylphosphatase (K-NPPase) activity of the Na-K-ATPase complex is introduced. The incubation medium contains p-nitrophenylphosphate (NPP) as substrate, lead citrate as the capture reagent, and dimethylsulfoxide (DMSO) as an activator. It is usable at the optimal pH of the K-NPPase, which is about pH 9.0 in the presence of 25% of DMSO. The effects of fixation, lead concentration, and DMSO on the enzyme activity were studied using rat kidney as a test tissue. The fixation of tissues in a mixture of 2% paraformaldehyde and 0.5% glutaraldehyde for 60 min at 0 degrees--4 degrees C preserved 45% of the enzyme activity. In the absence of DMSO, lead citrate (4.0 mM) caused 82% inhibition of the enzyme activity in fixed tissue. However, the addition of DMSO (25%) caused about 3-fold activation of the remaining activity. Cytochemical demonstration of the ouabain-sensitive K-NPPase activity was successfully made by this method at both light and electron microscopic levels.
187 citations
TL;DR: An exoribonuclease producing 5'-mononucleotides has been purified from ribosomes of Saccharomyces cerevisiae, and evidence for a 5' leads to 3' mode of hydrolysis is provided by a study of the products of the Hydrolysis of [3H](pA)5 labeled at the 5' termini with 32P.
TL;DR: Two 3-hydroxyacyl-CoA dehydrogenase enzymes in rat liver, one in mitochondria, and another in peroxisomes, were purified and compared for their properties to be completely different enzymes.
TL;DR: The elastase produced by Pseudomonas aerughosa is probably responsible for the tissue destruction observed during pulmonary and corneal infections by this pathogen, and a new substrate, AbzAla-Gly-Leu-AlA-Nba, is synthesized, which indicates that P. aeruginosaElastase in common with porcine pancreatic elast enzyme has an extended substrate recognition site.
TL;DR: It appears that Zn2+ does not participate in substrate binding nor in the maintenance of the quaternary structure of the enzyme, and Cd2+ was the only other element found which restored activity to the apoenzyme.
TL;DR: Evidence is presented that human carboxyl ester hydrolase is the lyophosphatidyl-choline-hydrolyzing enzyme corresponding to bovine lysophospholipase, in addition to the role of detergent that they have on insoluble substrates.
TL;DR: The consequences of changes in substrate concentration, in temperature, and in the effective kinetic parameters of transport and phosphorylation on rates of uptake demonstrate the complexity of this interdependence and the errors of interpretation that can accrue if the complexity is overlooked.
Abstract: Publisher Summary Three main classes of nutrients—nucleosides, nucleobases, and hexoses (and possibly a fourth, the water-soluble vitamins)—are taken up into cultured cells as a result of the tandem action of a nonconcentrative transport system and an intracellular enzyme that introduces into the transported substrate an anionic group thus confering impermeability. For several substrates representing the first three of these nutrient classes, both members of the uptake pathway are characterized kinetically: (1) the transport systems with cells and substrates that, by virtue of enzyme deficiency, adenosine triphosphate (ATP) depletion, or chemical design, are metabolically inert and (2) the enzymes, as purified proteins, in idealized milieu. The consequences of changes in substrate concentration, in temperature, and in the effective kinetic parameters of transport and phosphorylation on rates of uptake demonstrate the complexity of this interdependence and the errors of interpretation that can accrue if the complexity is overlooked. Flux in a tandem pathway follows a biphasic time course. The first phase corresponds to the attainment of steady-state levels of free intracellular substrate. The second phase represents steady-state flux through the pathway—that is, the rate of accumulation of impermeable product.
TL;DR: This enzyme may be related to the regulation of substance P in the brain, and to the development of neurones by forming the tetrapptide because the tetrapeptide has almost the same effect as substance P on the neurite extension of neuroblastoma.
Abstract: We determined changes in prolyl endopeptidase activity in developing rat brain. A new and highly sensitive fluorogenic substrate, 7-(succinyl-Gly-Pro)-4-methylcoumarinamide, was used for determination of the enzyme activity. The enzyme activity per brain increased until 2 weeks of age, and then decreased during maturation. The enzyme was purified about 7800-fold from the brain of the rat at 2 or 3 weeks of age. The enzyme has a pH optimum of 5.8 to 6.5, and an approximate molecular weight of 70,000. The enzyme activity was completely inhibited by low concentrations of diisopropylfluorophosphate and partially inhibited by high concentrations of phenylmethanesul-phonylfluoride, which are potent serine protease inhibitors. Moreover, thiolblocking agents and some heavy metals also have a strong effect on the activity. Bacitracin was found to be a potent inhibitor, with an IC50 value of 2.5 × 10−6m at 0.5 mm of the substrate. The enzyme was proved to hydrolyze the NH2-terminal tetrapeptide, Arg1-Pro2-Lys3-Pro4, from substance P to produce the heptapeptide, Gln5-Gln6-Phe7-Phe8-Gly9-Leu10-Met11-CONH2. The Km value of the hydrolysis of substance P was 1.0 mm. This enzyme may be related to the regulation of substance P in the brain, and to the development of neurones by forming the tetrapeptide because the tetrapeptide has almost the same effect as substance P on the neurite extension of neuroblastoma.
TL;DR: The results suggest that the catalytic activity of tryptophan hydroxylase is dependent on the oxidation-reduction status of--SH groups and iron sites, which are probably located at the catalysttic (substrate binding) site of the enzyme.
TL;DR: Evidence was obtained strongly suggestive of a quinonoid species as the primary product formed upon oxygenative defluorination of p-hydroxybenzoate derivatives, consistent with an oxenoid mechanism of oxygen attack.
TL;DR: A cellobiohydrolase component was isolated from a Penicillium funiculosum cellulase preparation by chromatography on DEAE-Sephadex, and purified by isoelectric focusing, and had little hydrolytic activity to highly ordered celluloses such as cotton fibre but, when recombined in the original proportions with the other components of the complex, 98% of the original activity was recovered.
Abstract: 1. A cellobiohydrolase component was isolated from a Penicillium funiculosum cellulase preparation by chromatography on DEAE-Sephadex, and purified by isoelectric focusing. 2. Purified in this way, the enzyme was homogeneous as judged by electrophoresis on sodium dodecyl sulphate/polyacrylamide gels and isoelectric focusing in polyacrylamide gels. 3. Acting in isolation, the enzyme had little hydrolytic activity to highly ordered celluloses such as cotton fibre, but, when recombined in the original proportions with the other components [endo-(1 leads to 4)-beta-D-glucanase and beta-D-glucosidase] of the complex, 98% of the original activity was recovered. 4. Synergistic effects were also observed when the enzyme was acting in concert with endo-(1 leads to 4)-beta-D-glucanase from other fungal sources. 5. Less-well-ordered celluloses, such as that swollen in H3PO4, were extensively hydrolysed, the principal product being cellobiose. 6. Attack on carboxymethyl-cellulose (CM-cellulose), which is the substrate normally used to assay for endo-(1 leads to 4)-beta-D-glucanase activity, was minimal. 7. The enzyme was associated with 9% of neutral sugar, 88% of which was mannose. It was isoelectric at pH 4.36 (4 degrees C) and had a mol.wt. of 46 300 (determined by gel chromatography on a calibrated column of Ultrogel). 8. The enzyme was specific for the beta-(1 leads to 4)-linkage.
TL;DR: The infrared spectrum of dihydroxyacetone phosphate bound to triosephosphate isomerase has been measured, providing direct evidence of enzyme-induced distortion of the substrate.
Abstract: The infrared spectrum of dihydroxyacetone phosphate bound to triosephosphate isomerase has been measured. There are two carbonyl bands corresponding to the bound substrate, with an intensity ratio of about 3:1. Relative to the carbonyl absorption of dihydroxyacetone phosphate in free solution, the major band is shifted by 19 cm-1 to 1713 cm-1, providing direct evidence of enzyme-induced distortion of the substrate. This strain is probably attributable to an enzymic electrophile that polarizes the carbonyl group of the substrate and thereby promotes catalysis.
TL;DR: In this paper, the effect of different substrate materials on crystallographic orientation was also described, and the maximum crystal orientation was found to occur with substrate temperatures between 325 and 400°C.
Abstract: Zinc oxide films, with a high degree of c‐axis orientation, have been grown on glass substrates by a chemical vapor deposition process involving the oxidation of diethylzinc. Film growth was carried out over the 200–500 °C temperature range; however, the maximum crystal orientation was found to occur with substrate temperatures between 325 and 400 °C. The effect of different substrate materials on crystallographic orientation is also described in this letter.
TL;DR: These experiments demonstrate that at a concentration of 20 μM, dopamine (DA) was the best substrate examined and was followed in decreasing order of activity by 3‐methoxytyramine (3‐MT), tyramine, norepinephrine and octopamine, 5‐hydroxytryptamine and dihydroxyphenylethyleneglycol, which became the most rapidly conjugated substrate at a substrate concentration of 100 /UM.
Abstract: Phenol sulfotransferase was isolated in 100,000g supernatant fractions prepared from postmortem samples of human brain. Since phenol sulfotransferase (PST) has been shown to conjugate the amine neurotransmit-ters in vivo, the abilities of eight different biogenic amines and structurally related compounds to act as substrates for PST were studied. These experiments demonstrate that at a concentration of 20 μM, dopamine (DA) was the best substrate examined and was followed in decreasing order of activity by 3-methoxytyramine (3-MT), tyramine, norepinephrine, 3-methoxy-4-hydroxyphenylethyleneglycol, octopamine, 5-hydroxytryptamine and dihydroxyphenylethyleneglycol. At a substrate concentration of 100 /UM the relative order of activity was altered, so that tyramine became the most rapidly conjugated substrate while the activity of DA and 3-MT relative to the other substrates tested was diminished. This change in substrate affinity with differing substrate concentrations can be explained, at least for DA, by the occurrence of apparent substrate inhibition at concentrations above 25 to 30 μM. Using PST isolated in 100,000g supernatant fractions from human brain, the Km value for DA was found to be 5.0 μM, while the Km value for the sulfate-donor 3′-phosphoadenosine-5′-phosphosulfate was 0.25 μM. The ratio of 3-O- to 4-O-DA-sulfate formed in vitro by human brain PST was found to be about 4: 1. In addition, both the 3-O- and 4-O-esters were found not to be deaminated by human brain mitochondrial MAO. The relative role of PST with respect to MAO and catechol-O-methyltransferase in the degradation of the biogenic amine neurotransmitters in human brain is discussed.
TL;DR: Starting from enzyme kinetics, it is shown that generally a linear rather than a proportional relationship exists between rate and free energy changes in biochemical processes.
TL;DR: The kinetics of the inactivation of Bacillus cereus beta-lactamase I by 6 beta-bromopenicillanic acid are described and it is shown that all of the above changes probably have the same rate-determining step.
Abstract: The kinetics of the inactivation of Bacillus cereus beta-lactamase I by 6 beta-bromopenicillanic acid are described. Loss of beta-lactamase activity is accompanied by a decrease in protein fluorescence, by the appearance of a protein-bound chromophore at 326 nm, and by loss of tritium from 6 alpha-[3H]-6 beta-bromopenicillanic acid. It is shown that all of the above changes probably have the same rate-determining step. The inactivation reaction is competitively inhibited by cephalosporin C, a competitive inhibitor of this enzyme, and by covalently bound clavulanic acid, suggesting that 6 beta-bromopenicillanic acid reacts directly with the beta-lactamase active site. It is proposed that this inhibitor reacts initially as a normal substrate and that the rate-determining step of the inactivation is acylation of the enzyme. A rapid irreversible inactivation reaction rather than normal hydrolysis of the acyl-enzyme then follows acylation; 6 beta-bromopenicillanic acid is thus a suicide substrate.
TL;DR: Ascorbate was found to be a quite specific requirement for lysyl hydroxylase, but the enzyme catalyzed its reaction for a short time at a high rate in the complete absence of this vitamin, suggesting that the reaction with ascorbates does not occur during each catalytic cycle.
TL;DR: In this article, the adsorption of cellulases from Trichoderma viride was studied during the hydrolysis of newspaper, and it was found that in the early stage of the process, enzyme components showing C/sub x/A were adsorbed preferentially to those showing c/sub 1/A; afterwards this situation was inverted.
Abstract: The adsorption of cellulases from Trichoderma viride was studied during the hydrolysis of newspaper. By measuring individual enzyme activities it was found that in the early stage of hydrolysis enzyme components showing C/sub x/A were adsorbed preferentially to those showing C/sub 1/A; afterwards this situation was inverted. Electrophoretic resolution of proteins in hydrolysates showed a continuous decrease of enzyme proteins in solution, and furthermore suggested that the enzymes once adsorbed remained immobilized on the substrate (even after extensive digestion). Experiments to recover the enzymes that had remained in solution after typical hydrolysis showed a potential saving of enzyme of up to 40%.