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Biomedical subjects

R E Childs

Publications and source records attributed to R E Childs.

13 recordsLinked to original sources
PubMed1976

A new method for deriving steady-state rate equations suitable for manual or computer use.

A schematic method for the derivation of steady-state enzyme rate equations by using the Wang algebra is described. The method is simple, easy to learn and offers a substantial decrease in analytical effort over previously published algorithms. Being essentially an algebraic procedure the method can be readily computerized. Computer programs in BASIC and ALGOL languages have been deposited as Supplementary Publication SUP 50065 (19 pages) at the British Library (Lending Division), Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1976). 153, 5.

Computers↗
PubMed1976

Peroxidase from human cervical mucus. The isolation and characterisation.

A peroxidase has been isolated from pooled specimens of human cervical mucus. Investigation of substrate and inhibitor specificity, pH optimum, chromatography on Sephadex G-200, disc electrophoresis, ultraviolet absorption spectrum and the effects of temperature and ionic strength variation are described. A study of the steady-state kinetics is reported using hydrogen peroxide and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) as substrates and a catalytic mechanism is proposed.

Cervix Mucus↗
PubMed1975

Time-dependent inhibition of diamine oxidase by carbonyl-group reagents and urea.

1. The behaviour of several carbonyl group reagents and urea as time-dependent inhibitors of both pig kidney and human placental diamine oxidase is described. 2. Plots of log (vt/vo) against time were not linear with these reagents as the usual theories predict. 3. This was particularly the case with aminoguanidine and phenylhydrazine and a thorough study of the effects of these compounds on the human placental diamine oxidase is described. 4. By applying a new theory for time-dependent inhibition, the inhibition of diamine oxidase by aminoguanidine and phenylhydrazine is adequately accounted for. 5. The time-dependent recovery of activity on addition of sodium pyruvate suggested that the compounds used are acting solely as carbonyl group reagents, inhibiting by Schiff-base formation at the active-site carbonyl group.

Amine Oxidase (Copper-Containing)↗
PubMed1975

The steady-state kinetics of peroxidase with 2,2'-azino-di-(3-ethyl-benzthiazoline-6-sulphonic acid) as chromogen.

The chemical nature of the important new chromogen ABTS [2,2'-azino-di-(3-ethyl-benzthiazoline-6-sulphonic acid)] is described together with an account of the redox and spectroscopic properties of the system ABTS--H2O2--peroxidase. Keq. is calculated and a study of the steady-state kinetics over a whole range of substrate concentrations is reported. By using novel methods of kinetic analysis, an interpretation of the results is given which requires some extension of the classical peroxidase mechanism.

Benzothiazoles↗
PubMed1975

Sigmoid curves, non-linear double-reciprocal plots and allosterism.

1. The theory of plane curves was applied to the graphical methods used in enzyme kinetics and a mathematical analysis of the possible graph shapes is given. 2. The belief that allosterism can be inferred from steady-state data alone is subjected to criticism and the mathematical significance of sigmoid curves and non-linear double-reciprocal plots is explored. 3. It is suggested that the usual methods of interpreting steady-state kinetic data are often based on over-restrictive assumptions which prevent maximum utilization of the available data. 4. Methods for obtaining the degree of the rate equation from graph shapes obtained directly from initial-rate measurements and from replots of asymptotic behaviour as chi approach the level 0 and chi approach the level infinity are discussed. 5. Detailed proofs of the theorems given in the text have been deposited as Supplementary Publication SUP 50049 (10 pages) at the British Library (Lending Division), Boston Spa, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1975), 145, 5.

Allosteric Regulation↗
PubMed1974

Inhibition of enzymes by metal ion-chelating reagents. Theory and new graphical methods of study.

1. The mechanism of inhibition of enzymes by metal ion-chelating reagents is discussed and equations derived. 2. Two distinct mechanisms are postulated and graphical methods are given for differentiating between them. 3. Where the metal ion is actually removed from the enzyme to form a co-ordination complex in solution, a procedure is described for obtaining the stability constant for metal-enzyme interaction, the number of metal ions involved and the stoicheiometry of metal ion-ligand interaction.

Binding Sites↗
PubMed1974

Inhibition of enzymes by metal ion-chelating reagents. The action of copper-chelating reagents on diamine oxidase.

1. The inhibition of diamine oxidase has been studied by using the following copper-chelating reagents: 1,10-phenanthroline; 2,2'-bipyridyl; 8-hydroxyquinoline (oxine); diethyldithiocarbamate and dithio-oxamide (rubeanic acid). 2. Addition of chelating reagent caused a rapid inhibition of enzyme to a degree dependent solely on the final inhibitor concentration. Addition of substrate gave linear initial rates of reaction showing that under these conditions the inhibition was not being rapidly reversed. 3. The inhibition has been investigated by using new graphical methods and has been found in all cases to involve the chelating agents completely removing two Cu(2+) ions from the enzyme. An alternative possibility, involving ligand substitution, was eliminated. 4. A value of K=8.0x10(-33)m(-2) has been found for the enzyme in equilibrium with 2 Cu(2+) ions (i.e. beta(2), the stability constant for diamine oxidase/two Cu(2+), is 32.1).

Amine Oxidase (Copper-Containing)↗