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I946 cysteine (as ethyl ester); other experiments gave similar results; the inactivation with the-S-S compound and reactivation with-SH was definite. DISCUSSION Systematic investigations upon-SH groups in an enzyme appear to have been first made upon urease by Hellerman, Perkins & Clark (1933) (see Hellerman, 1937). Some facts as to the action of maleate upon brain tissue have already been published by Weil-Malherbe (1938), who quoted earlier literature. He found that 20 mM-maleic acid inhibited the respiration of brain slices in bicarbonate-glucose-Ringer by 10-50 %; the inhibition was comparatively small in presence of pyruvate, and it thus appears that the pyruvate oxidase system is even less sensitive in the slice than in the brei. Our facts are consistent with the idea that an-SH group is essential for the activity of this system, and that this group is so activated as to be specially sensitive to maleate. It is still necessary to qualify this by pointing out that the evidence is indirect, because the enzyme concerned has not yet been obtained in pure form; the evidence has been much strengthened by the dithiol theory of Stocken & Thompson (1940-41) (for a brief account see Peters, Stocken & Thompson, 1945). (Recently, Barron & Singer (1945), see also Waters & Stock (1945), have also concluded that the pyruvate oxidase system is specially sensitive to-SH reagents; independently Bacq (1942) has found the-SH fraction in proteins abolished by some vesicants.) SUMMARY 1. Arising from earlier work on chemical warfare agents, and from a research upon antidotes, the sensitivity of the pyruvate oxidase system from brain to some-SH reagents was investigated. 2. The pyruvate oxidase system and the pyruvate dehydrogenase component were much more sensitive to sodium maleate than succinodehydrogenase. Pyruvate dehydrogenase was inactivated by cystine ester and reactivated by cysteine ester. Both these effects are explained by the presence of an essential-SH group in the enzyme concerned. We are grateful to Dr L. A. Stocken for the preparations of the esters of cystine and cysteine (as hydrochloride).

second, increased deposition of muscle glycogen; third, increased glucose use in the tissues; and fourth, conversion to fat.In the non-diabetic rat salicylate caused no change in blood glucose, but a significant reduction of liver glycogen and similar mechanis may be involved. The possibility that the glucose may be converted to glucuronic acid which is used for conjugation with salicylate is unlikely because of Lutwak-Mann's (1942) conclusion that the ability of rat liver to form a conjugated glucuronide from salicylate was negligible.It is proposed to extend this work to investigate the possibilities discussed above. SUMMARY 1. The effect of salicylate on the glycosuria, blood glucose and liver-glycogen content of the alloxan-diabetic rat and on the blood glucose and liver glycogen of the normal rat have been studied.2. Salicylate reduces the glycosuria and blood glucose in the diabetic rat, but causes no change in the liver-glycogen content. In the normal rat salicylate causes no alteration in the blood glucose, but a depression of the liver-glycogen content. 3. Possible mechanisms of these changes are discussed.We wish to express our thanks to Miss M. Sandiford and Miss E. Quilley for able technical assistance. One of us (M.J.H.S.) is indebted to the Board of Governors of King's College Hospital for a grant towards the cost of the work.

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THE discovery by Lohmann & Schuster [1937] that cocarboxylase is the pyrophosphoric ester of vitamin B1 suggested that in animal tissues the vitamin is active like this ester in the oxidation of pyruvic acid. It now seems clear that animal tissues and certain bacteria do not decarboxylate pyruvic acid to acetaldehyde and CO2 (as yeast does) but instead oxidize it to acetic acid and C02, either by dismutation under anaerobic conditions or directly [Krebs & Johnson, 1937; Lipmann, 1937, 1; Weil-Malherbe, 1937]. Lipmann [1937, 2] reports that with acetone preparations from B. Delbruickii the simultaneous decarboxylation and oxidation of pyruvic acid require cocarboxylase.In animal tissues evidence that vitamin B1 pyrophosphate is concerned in the oxidation of pyruvic acid is derived (1) from catatorulin tests, and (2) from the presence of cocarboxylase in tissues and their alleged capacity to synthesize cocarboxylase from vitamin B1. The first point, that cocarboxylase can replace vitamin B1 in catatorulin tests [Lohmann & Schuster, 1937], has not been confirmed in this laboratory using "teased" brain [Peters, 1937]; more recent unpublished experiments with brain slices also gave negative results. This point obviously requires further elucidation.In regard to the second point, Auhagen [1932] first showed that boiled extracts of animal tissues stimulated the decarboxylation of pyruvic acid by yeast preparations (aetiozymase), indicating the presence of cocarboxylase. Simola [1932] investigated the influence of nutrition upon this phenomenon. Synthesis of cocarboxylase from vitamin B1 by minced animal tissues or various tissue preparations has been reported from several laboratories [von Euler & Vestin, Hofer [1937] reported negative results. This work is not yet sufficiently quantitative and further it has not so far been ascertained whether vitamin B1 is present in tissues in the free form.We have now developed a method which allows the separate quantitative estimation of cocarboxylase and free vitamin B1, by means of which the following points have been investigated: (1) the cocarboxylase and vitamin B1 contents of boiled extracts from normal and avitaminous tissues, (2) the enzymic synthesis of cocarboxylase from vitamin B1. In the present paper we shall show that there is much more cocarboxylase than vitamin B1 present in animal tissues, and that it is much reduced when vitamin B1 is withheld from the diet, and further, that the liver readily synthesizes cocarboxylase from vitamin B1 in vivo. Another paper will deal with the synthesis of cocarboxylase in vitro. Various organs (brain, muscle) have only a very limited power of synthesis ;2 intestinal mucosa does not show any activity at all, whereas active preparations can be obtained from the liver. 1 A preliminary report of this work appeared in the Tran8. Soc. Chem. Ind. 57, 470, 1938. 2 Less in the case of brain than suggested by Peters [1937], who did not know of the stimulating effect of vitamin B1 upon the action of cocarboxylase (cf. below).( 1501 )