Search PubMed⌕ Search

Biomedical subjects

K J Laidler

Publications and source records attributed to K J Laidler.

At least 19 recordsLinked to original sources
PubMed2001

Alcohol and violence in the lives of gang members.

Life within a gang includes two endemic features: violence and alcohol. Yet, to date, most researchers studying gang behavior have focused on violence and its relationship to illicit drugs, largely neglecting the importance of alcohol in gang life. Because alcohol is an integral and regular part of socializing within gang life, drinking works as a social lubricant, or social glue, to maintain not only the cohesion and social solidarity of the gang, but also to affirm masculinity and male togetherness. In addition to its role as a cohesive mechanism, particular drinking styles within gangs may operate, as with other social groups, as a mechanism to maintain group boundaries, thereby demarcating one gang from another. Other examples of internal gang violent activities associated with drinking include fighting between members because of rivalries, tensions, or notions of honor or respect. At a more symbolic level, drinking is associated with two important ritual events in gang life: initiation, or "jumping in,"and funerals. By better understanding the link between drinking and violence among youth gangs, steps can be taken to determine the social processes that occur in the development of violent behavior after drinking.

Adolescent↗
PubMed1986

Flow kinetics of immobilized beta-glucosidase.

The enzyme beta-glucosidase was attached covalently to the inner surface of nylon tubing. Flow kinetic studies were carried out at a range of temperatures, pH values, flow rates, and substrate concentrations. Various tests showed that the extent of diffusion control was negligible. At 25 degrees C the Michaelis constant was 33.4 mM, not greatly different from the value for the enzyme in free solution. The pH dependence was similar to that for the free enzyme. The Arrhenius plots showed inflexions at about 22 degrees C, as with the free enzyme, the changes in slope being small at the pH optimum of about 5.9 and becoming much more pronounced as the pH is increased or decreased. The immobilized enzyme is more stable than the free enzyme, both on storage at low and higher temperatures, and its reuse stability is greater.

Calorimetry↗
PubMed1983

Thermodynamic profiles for alcohol dehydrogenase action in free solution.

Stopped-flow equipment was used to study the kinetics of the reaction between nicotinamide adenine dinucleotide (NAD) and ethanol, catalyzed by yeast alcohol dehydrogenase. By measuring rates over a range of concentrations of NAD and ethanol and of temperatures, thermodynamic profiles were obtained for the reaction, which occurs by an ordered ternary complex mechanism with NAD adding first. There are significant negative entropies of activation and negative entropy changes for the addition of NAD and of ethanol; the breakdown of the ternary complex is, however, accompanied by a positive entropy of activation. The results are consistent with structural constraints associated with the binding of the substrates, these restraints being to some extent removed when the ternary complex undergoes reaction. The system follows a similar pattern to that found with three different varieties of lactate dehydrogenase.

Alcohol Oxidoreductases↗
PubMed1983

Kinetic equations and mechanisms for activation and inhibition in enzyme systems.

The rates of enzyme reactions that are activated or inhibited by added modifiers can in some cases be expressed as a rational function of the first degree, v = (alpha 0 + alpha 1[Q] )/(beta 0 + beta 1 [Q] ) where [Q] is the concentration of the modifier and alpha 0, alpha 1, beta 0, and beta 1 are functions of rate constants and sometimes of the enzyme and substrate concentrations; the behaviour is then said to be linear. Three simple mechanisms that give rise to linear kinetics are examined, and the conditions under which there is activation or inhibition are determined. Sometimes there is a transition from activation to inhibition as the substrate concentration is varied. Definitions of competitive, uncompetitive, and noncompetitive activation are suggested, by analogy with the generally accepted definitions for inhibition. In second-degree activation or inhibition the rate can be expressed as the ratio of two quadratic polynomials with positive coefficients. Ten patterns are then possible for plots of v against [Q], and they may be classified with respect to (i) overall activation or inhibition, (ii) initial (at [Q] leads to 0) activation or inhibition, (iii) terminal (at [Q] leads to oo) activation or inhibition, and (iv) whether there is an initial inflexion. The general case of an n:n rational function is also discussed.

Enzyme Activation↗
PubMed1982

pH dependence of free and immobilized yeast alcohol dehydrogenase kinetics.

A study was made of the influence of pH on the reaction between NAD and ethanol, catalyzed by yeast alcohol dehydrogenase, both in free solution and attached to the inner surface of a nylon tube. A new least-squares analysis of the results has been devised; it is simpler to apply and is more realistic than those previously employed. Analysis of the results for the free enzyme indicated that the free enzyme has two active ionizing groups having pK values of about 6.6 and 8.8. These pK values undergo only small changes when the enzyme is bound to NAD and when it is bound to both NAD and ethanol. With the immobilized enzyme and saturating concentrations of ethanol the rates went through a maximum as the pH was varied from 6.5 to 10.0. With saturating concentrations of NAD there was a steady increase in rate, with no falling off at pH 10. Immobilization generally brought about an increase in the pK values. These increases are attributed partly to a residual negative surface charge which attracts the leaving H+ ions. They are also attributed partly to the formation in the reaction of H+ ions, which cause the local pH to be lower than that in the bulk solution. This effect is more important with saturating NAD ions, since the buffer anions will then be less mobile and less able to mediate the movement of protons.

Alcohol Dehydrogenase↗
PubMed1980

Flow kinetics of yeast alcohol dehydrogenase attached to nylon tubing.

Yeast alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) was attached covalently to the inner surface of nylon tubing, and the immobilized enzyme retained its activity over a period of months. A study was made of the flow kinetics for the reaction between ethanol and NAD. With the ethanol held at saturating concentrations there was partial diffusion control, the extent decreasing with increasing flow rate and increasing NAD concentration. With the NAD at saturating concentrations there was no appreciable diffusion control. The apparent Michaelis constants varied with flow rate vf, being linear in vf-1/3, and extrapolation to infinite flow rate (vf-1/3 = 0) gave the intrinsic Michaelis constants. The inhibition by products was also studied. The results for both NADH and acetaldehyde showed mixed competitive and non-competitive inhibition, with a preponderance of the former. Acetaldehyde is the stronger inhibitor, and this is consistent with the lack of dissusion control with variable ethanol. Inhibition by acetaldehyde is not affected by flow rate, but inhibition by NADH is affected, presumably because of the greater degree of diffusion control with variable NAD.

Alcohol Oxidoreductases↗
PubMed1980

Temperature and pH effects on immobilized lactate dehydrogenase kinetics.

Rabbit muscle lactate dehydrogenase (EC 1.1.1.27) was attached covalently to the inner surface of nylon tubing, and kinetic measurements made. The results were interpreted on the basis of the Kobayashi-Laidler treatment of immobilized enzymes in flow systems, various tests being applied to determine the degree of diffusion control. It was established in various ways that the degree of diffusion control increases with (a) decrease in flow rate, (b) decrease in substrate concentration, and (c) decrease in temperature. A number of quantitative relationships, predicted by the theory, were obeyed by the results, for example: (a) Km(app) varies linearly with vf-1/3, where vf is the flow rate, (b) the logarithm of the product concentration at the exit varies linearly with the logarithm of the flow rate, and (c) absolute calculations of product concentrations are in reasonable agreement with experiment. A value of 5 kcal . mol-1 is estimated for the activation energy of the diffusion processes, and of 1 kcal . mol-1 for the chemical processes. When the pH is varied the rates pass through a flat maximum, the pH dependence being less than with the free enzyme.

Animals↗
PubMed1979

The reactivity of tryptophan residues in proteins. Stopped-flow kinetics of fluorescence quenching.

The quenching of tryptophan fluorescence by N-bromosuccinamide, studied by the fluorescence stopped-flow technique, was used to compare the reactivities of tryptophan residues in protein molecules. The reaction of N-bromosuccinamide with the indole group of N-acetyltryptophanamide, a model compound for bound tryptophan, followed second-order kinetics with a rate constant of (7.8 +/- 0.8) . 10(5) dm3 . mol-1 . s-1 at 23 degrees C. The rate does not depend on ionic strength or on the pH near neutrality. The non-fluorescent intermediate formed from N-acetyltryptophanamide on the reaction with N-bromosuccinamide appears to be a bromohydrin compound. The second-order rate constant for fluorescence quenching of tryptophan in Gly-Trp-Gly by N-bromosuccinamide was very similar, (8.8 +/- 0.8) . 10(5) dm3 . mol-1 . s-1. Apocytochrome c has the conformation of a random coil with the single tryptophan largely exposed to the solvent. The rate constant for the fluorescence quenching of the tryptophan in apocytochrome c by N-bromosuccinamide was (3.7 +/- 0.3) . 10(5) dm3 . mol-1 . s-1. The fluorescence quenching by N-bromosuccinamide of the tryptophan residues incorporated in alpha-chymotrypsin at pH 7.0 showed three exponential terms from which the following rate constants were derived: 1.74 . 10(5), 0.56 . 10(5) and 0.11 . 10(5) dm3 . mol-1 . s-1. This protein is known to have eight tryptophan residues in the native state, six residues at the surface, and two buried. Three of the surface tryptophans have the indole rings protruding out of the molecule and may account for the fastest kinetic phase of the quenching process. The intermediate phase may be due to three surface tryptophans whose indole rings point inwards, and the slowest to the two interior tryptophan residues.

Absorption↗
PubMed1979

Kinetics of acetylcholinesterase immobilized on polyethylene tubing.

Acetylcholinesterase was covalently attached to the inner surface of polyethylene tubing. Initial oxidation generated surface carboxylic groups which, on reaction with thionyl chloride, produced acid chloride groups; these were caused to react with excess ethylenediamine. The amino groups on the surface were linked to glutaraldehyde, and acetylcholinesterase was then attached to the surface. Various kinetic tests showed the catalysis of the hydrolysis of acetylthiocholine iodide to be diffusion controlled. The apparent Michaelis constants were strongly dependent on flow rate and were much larger than the value for the free enzyme. Rate measurements over the temperature range 6-42 degrees C showed changes in activation energies consistent with diffusion control.

Acetylcholinesterase↗
PubMed1978

Temperature and pH effects with immobilized electric eel acetylcholinesterase.

Kinetic studies were made with 2 forms of immobilized acetylcholinesterase: enzyme trapped in polyacrylamide gel which was cut into slices; and enzyme attached to the inner surface of nylon tubing. Rates were measured at substrate concentrations which were low and high with reference to the Michaelis constant, and over the temperature range 16-40 degrees C. Low activation energies (1.7-2.7 kcal mol-1) were obtained at low substrate concentrations, indicating diffusion control. At high substrate concentrations the Arrhenius plots were non-linear and the activation energies substantially higher, and there is less diffusion control. With enzyme-polyacrylamide slices, there was a continuous increase in rate with increasing pH, in contrast to the bell-shaped behavior with free enzyme. A theoretical treatment suggests that this is due to the lowering of local pH as a result of the acid released in the hydrolysis.

Acetylcholinesterase↗
PubMed1978

Flow kinetics of lactate dehydrogenase chemically attached to nylon tubing.

Rabbit muscle lactate dehydrogenase (EC 1.1.1.27) was attached covalently to the inner surface of nylon tubing; a modified technique, involving benzidine and glutaraldehyde, was used, and the resulting immobilized enzyme showed no loss of activity over a period of several months. An experimental study was made of the flow kinetics for the reaction between pyruvate and reduced nicotinamide adenine dinucleotide in two limiting cases, one substrate in excess and the concentration of the other one varied. A range of flow rates and temperatures was covered. The results were analyzed in various ways on the basis of the Kobayashi--Laidler treatment of flow systems. It was concluded that the kinetics are largely diffusion-controlled, especially at the lower substrate concentrations and flow rates. The values of the apparent Michaelis constants vary with flow rate vf, being linear in vf-1/3, and the values extrapolated to infinite flow rate (vf-1/3 = 0) approach the values for the enzyme in free solution. Analysis of the rates led to activation energies for the diffusion of the two substrates.

Enzymes, Immobilized↗
PubMed1976

Hydrolysis of D-galactosides in an open tubular lactase reactor.

Lactase (beta-galactosidase) was attached to the inner surface of nylon tubing. Tubes of various lengths were used to bring about the hydrolysis of o-nitrophenyl-beta-D-galactoside and of lactose in skim milk. The results with the former substrate were analyzed in the light of a theoretical treatment of Kobayashi and Laidler (Biotechnol. Bioeng., 16, 99, 1974), with the conclusion that the reaction is intermediate between diffusion-free and completely diffusion-controlled behavior. The results with skim milk show that with a single 46 m tube and continuous circulation, 90% of the lactose is removed within 20 hr. A battery of ten such tubes, with single passage, at a flow rate of 2 cm/sec, would remove more than 99% of the lactose in less than 40 min.

Animals↗
PubMed1976

Four-and five-step kinetic models of lactate dehydrogenase.

A five-step model for the reaction catalyzed by beef heart lactate dehydrogenase (EC 1.1.1.27) reconciles differences observed in the four-step model if pre-steady-state data in the forward direction are compared with similar data in the reverse direction. The relationship between the four-and five-step models indicates what problems can develop when an incomplete model is proposed. Nevertheless, there are advantages to using the less complicated four-step model when comparing the molecular kinetics of enzymes catalyzing the same reaction but obtained from different sources.

Animals↗