Biomedical subjects
J S Shindler
Publications and source records attributed to J S Shindler.
Domperidone and levodopa in Parkinson's disease.
To study the absorption of levodopa and interaction with the extracerebral dopamine antagonist domperidone, 15 patients with idiopathic Parkinson's disease were given levodopa 500 mg p.o., alone, and with domperidone pre-treatment. Domperidone pretreatment (10, 20, 40 mg, p.o., i.v. or i.m.) caused a mean 12% increase in peak plasma levodopa concentration, which occurred a mean of 10 min earlier than when levodopa was given alone. Parkinsonian disability scores were improved and peak clinical response occurred 16 min earlier with domperidone than without. Domperidone slightly increases the immediate bioavailability (over 4 h) and anti-parkinsonian response to a given dose of levodopa.
Probing the limits of protein-amino acid side chain recognition with the aminoacyl-tRNA synthetases. Discrimination against phenylalanine by tyrosyl-tRNA synthetases.
The specificity of the tyrosyl-tRNA synthetases from Escherichia coli and bacillus stearothermophilus for tyrosine compared with phenylalanine has been determined by using samples of phenylalanine which have been scrupulously freed from tyrosine by either chemical or enzymic scavenging procedures. Both kinetic measurements and product analyses give a value of 1 x 10(5)-2 x 10(5) for the preferential activation of tyrosine. Combined with the known ratio of phenylalanine to tyrosine in rapidly growing E. coli, an error rate of about approximately 5/10(4) is calculated for the misactivation of phenylalanine. Since we find no evidence for an editing mechanism and this error rate is similar to observed rates in protein synthesis, the tyrosyl-tRNA synthetases appear to have adequate amino acid selection by simple preferential binding of the correct substrate. The incremental binding energy of the phenolic hydroxyl group of tyrosine is approximately 7 kcal/mol, a value presumed close to the maximum possible because of the evolutionary pressure on tyrosyl-tRNA synthetases for maximum specificity. A summary of high incremental binding energies determined from experiments on aminoacyl-tRNA synthetase is presented.
A quantitative plot for the determination of negatively co-operative ligand binding sites in proteins.
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A model for the allosteric regulation of pH-sensitive enzymes.
1. In an enzyme that has two independent binding sites for a ligand, any inhibitor that binds solely to the free enzyme will give rise to positive co-operativity. 2. A model is considered for the allosteric control of enzymes by effectors in which their effects are mediated by ligand-induced perturbations of the ionization constants of a group or groups involved in the binding of substrate to the active site. 3. The model described offers a plausible explanation for the observation that the sigmoidal initial-rate curves reported for some regulatory enzymes are not expressed at all pH values where the enzyme is catalytically active.
A study of peroxidase levels in human cervical mucus as an index of ovulation.
Fourteen healthy women were screened for the following parameters throughout one complete menstrual cycle: levels of urinary oestrogens and pregnanediol; levels of plasma and urinary gonadotrophins; and pH, protein content and levels of peroxidase in the cervical mucus. It was found that concentrations of peroxidase in the cervical mucus were not a reliable index of ovulation.
Human kidney diamine oxidase: inhibition studies.
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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.
Steady-state kinetics of lactoperoxidase with ABTS as chromogen.
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Kinetics of the diamine oxidase reaction.
1. The oxidation of p-dimethylaminomethylbenzylamine was followed spectrophotometrically by measuring the change in E(250) caused by the p-dimethylaminomethylbenzaldehyde produced under a wide variety of experimental conditions. 2. The effect of variations in concentrations of both substrates (amine and oxygen) and all products (aminoaldehyde, hydrogen peroxide and ammonia) on this reaction was studied and the results used to develop a formal mechanism. 3. The nature of the rate-limiting step was elucidated by studying the effects of alterations in ionic strength, dielectric constant and deuterium substitution on the velocity of the forward reaction. 4. Thermodynamic activation energy parameters were obtained at several pH values from the effects of temperature on the reaction.
Oxidation of p-dimethylaminomethylbenzylamine by pig kidney diamine oxidase. A new method for spectrophotometric assay.
1. The oxidation of some para-substituted benzylamines by diamine oxidase produces the corresponding aldehydes. This was studied to develop a spectrophotometric method for following the enzyme reaction, as the aldehydes produced absorb strongly at 250nm where the substrates are almost optically transparent. 2. p-Dimethylaminomethylbenzylamine was the most useful substrate and full details of its preparation are given. The synthesis of its related oxidation product, p-dimethylaminomethylbenzaldehyde, is also described. 3. The effects of variations in pH, ionic strength, temperature and oxygenation on the reaction are described and the usefulness of the method is illustrated by several applications and assessed by comparison with the standard spectrophotometric assay.