The role of sulphydryl groups of yeast carboxylase

The modes of action of toxic agents I. Observations on the poisoning of certain crustaceans by copper and mercury

“…Thus it has been found that Artemia which have been treated with a sublethal dose of mercuric chloride become more sensitive to poisoning by copper, and that this (sensitizing' effect can be appreciably reduced if the mercury-treated animals are washed with cysteine or with reduced glutathione. These experiments were similar in principle to those carried out by various workers in the course of studies of enzyme inhibition in which it was observed that the inactivation of enzymes such as urease (Hellerman, Chinard & Deitz, 1943),papain (Hellerman & Perkins, 1934) and yeast carboxylase (Stoppani, Actis, Deferrari &: Gonzalez, 1953)by small amounts of copper, mercury and various (mercaptide-forming' substances derivedfrom the latter (e.g.phenylmercuric chloride) could be partially reversed by thiol compounds such as cysteine. These findings have led to the view that heavy metal poisons inhibit these enzymes by attaching to the surfaces at sulphydryl groups responsible for catalytic activity.…”

Nutritional regulation of antennal/leg homoeotic mutants inDrosophila melanogaster

“…The degradation of fatty acids also gives rise to acetyl-CoA but since the defined medium contains no phospholipids this is unlikely to be an important acetyl-CoA source in these experiments. Stoppani et al (1953) examined the inhibition of yeast pyruvate dehydrogenase, and found that the purified enzyme is particularly sensitive to sodium arsenite. When arsenite was added to the defined medium there was a significant reduction in penetrance (Fig.…”

Essential role of thiol groups in aldehyde dehydrogenases

“…Effect of pyridine nucleotides on the inhibition of the yeast potassium-activated aldehyde dehydrogena8se by thiol reagents 0 9 mg. Effect of acetaldehyde on the inhibition of aldehyde dehydrogenases by thiol reagents Protection of many thiol enzymes by the substrate is a well-known phenomenon, e.g. succinic dehydrogenase by succinate (Hopkins, Morgan & Lutwak-Mann, 1938), alcohol dehydrogenase by ethanol (Barron & Levine,1952), glyceraldehyde 3-phosphate dehydrogenase by glyceraldehyde 3phosphate (Segal & Boyer, 1953) and carboxylase by pyruvate (Stoppani et al 1953). On these grounds a similar protection of the aldehyde dehydrogenases by the substrate has been investigated.…”