No abstract

No abstract

No abstract

I. With the object of producing standard low‐temperature burns in animals, and of studying the area of tissue only partly damaged in a burn, a burning iron has been made capable of applying temperatures from 45°‐80°C. to the skin; with this the amount of heat and temperature causing skin damage has been studied, and the macroscopic and microscopic damage due to graded temperatures have been delineated. II. Macroscopic Changes. 1. Graded temperatures of 45°‐80°C. have been applied to the skin of shaved, anæsthetised guinea‐pigs, and in some cases rats, for times varying from 10 sec. to 6 and 10 min. Observations have been made of the development of erythema, flare, blanching, blueing, heat fixation, incipient blister formation, œdema, and edge wheal, as also upon the later scab formation and rate of epithelium regeneration. 2. Applications of 47°C. up to 6 minutes produce no visible change. 3. At 50°‐55°C. applied for 1 minute and over, there is a critical temperature for the development of permanent and irreversible damage; in animals good scab formation occurs after burning at this temperature. 4. After temperatures of 60°‐65°C. the epidermis can be peeled off from the exposed area, leaving a punched‐out exposed surface area somewhat like the exposed human blister. 5. A temperature of 70°‐80°C. for 10‐20 seconds produces severe scabbing. 6. Observations of œdema formation have been checked by wet and dry weights of specimens of skin taken 2 hours after heating. At 55°C. there is some change, but this is more definite at 60°C. 7. The observations recorded here are readily reproducible and provide a standard method of burning for experimental work. III. Microscopic Changes. 1. The histological effects of mild burns of varying intensity and duration have been described in detail. They follow the general picture previously recorded in necrotic changes. 2. Two different types of reaction are described; with milder burns there is cellular disintegration; with more intense burns, heat coagulation. 3. In more intense burns there is a peripheral shell of changes characteristic of burns of lower temperature. 4. Two substances are lost by the epithelium of skin which has been subjected to a burn: (a) Basophil granules from the cytoplasm. (b) Nucleoprotein from the nuclei. These two substances can be identified in the intercellular blister spaces. 5. Collagen fibres change in structure and staining affinity in the more intense burns. Our thanks are due to the Carnegie Trustees for a personal grant to one of us (R. J. Rossiter); to the Nuffield Committee and Trustees and to the Medical Research Council for grants which have helped the cost of this research, though this has been also much financed from University sources. We are grateful to Dr. M. C. Manifold for help with some of the preliminary observations and to Dr. A. N. Drury, Dr. L. Colebrook, and Mr. E. Rock Carling for their interest. We also wish to thank Mr. Marsden for technical assistance with the histology.

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).

THE object of this paper is to present a final proof that the form of vitamin B1 active in pyruvic acid oxidation is the pyrophosphate and to show that C4 dicarboxylic acids are an essential part of this system. In so doing not only is the hypothesis of the German workers [Lohmann & Schuster, 1937] proved, but also the importance of recent Hungarian. work [Szent-Gyorgyi et al. 1936] fully substantiated. We may also consider that we know now the main facts about the biochemistry of vitamin B1.The discovery by Lohmann & Schuster [1937] that cocarboxylase is the pyrophosphate of vitamin B1, strongly suggested that the phosphoester was the form in which the vitamin is active in the oxidation of pyruvate in animal tissues. It .was pointed out in a previous paper [Ochoa & Peters, 1938, 1] that there were two main lines of evidence to support this view: (1) The presence of cocarboxylase in the tissues and the ability of tissues to phosphorylate vitamin B1;(2) the alleged activity of cocarboxylase in "catatorulin" tests with slices of avitaminous pigeon's brain. Further indirect support was given by the experiments of Lipmann [1937] who showed that the oxidative decarboxylation of pyruvic acid according to reaction (1) or its dismutation [Krebs & Johnson, 1937] according to reaction (2), by alkaline-washed preparations of lactic acid bacteria (Bacterium Delbriuckii), was. catalysed by the pyrophosphate but, not by free vitamin B1. More recently Barron & Lyman [1939] have confirmed this for various strains of gonococcus and staphylococcus.

BY the use of finely ground preparations (dispersions) of pigeon's brain in phosphate buffer, we have shown in a previous paper [Banga et al. 1939, 1] that cocarboxylase (vitamin B1 pyrophosphate) is the active form of vitamin B1 concerned with the oxidation of pyruvate in brain, and, further, that C4 dicarboxylic acids activate this oxidation in a catalytic manner. The action of succinate on the oxidative decarboxylation of pyruvate by washed muscle preparations had been observed shortly before by Annau & Erdos [1939]. We shall show in this paper that, upon dialysing the brain dispersions, not only does the effect of the C4 dicarboxylic acids become more definite, but the need for other substances in the oxidation system can also be demonstrated. This is the case with inorganic phosphate and "adenine nucleotide" (this term being here used to include adenylic acid and adenosine triphosphate). The necessity of "pyridine nucleotide" (cozymase) has been made likely. Further, it has been recently shown by Ochoa [1939] that magnesium (or manganese) ions are also indispensable components of the oxidation system. We now know that at least the following substances are components of the pyruvate oxidation system of brain and, probably, of other animal tissues: (1) cocarboxylase, (2) inorganic phosphate, (3) C4 dicarboxylic acids (succinate, fumarate, etc.), (4) "adenine nucleotide ", (5) Mg++ (or Mn++) and, probably, (6) cozymase (pyridine nucleotide). It will further be shown that citrate or other intermediates of the citric acid cycle of Krebs & Johnson [1937], such as cx-ketoglutarate, are much less active than C4 dicarboxylic acids in the pyruvate oxidation system of brain, thus making it very unlikely that oxidation of pyruvate in brain can take place through such a cycle. In another section the oxidation of phosphoglyceric acid by brain dispersions is studied. Phosphoglyceric acid is rapidly converted into pyruvic acid by the dispersions and is, therefore, readily oxidized. It has been found that the reactions Phosphoglyceric acid 2± Phosphopyruvic acid, Phosphopyruvic acid + Adenylic acid-+Pyruvic acid + Adenosine polyphosphate, take place in brain in the same way as in muscle. Experimental methods Brain dispersions were prepared by thoroughly grinding, in an ice-cold mortar, 1 part of tissue with 4 parts of ice-cold 0*9 % KCI; the mixture was then pressed through muslin. The dispersion was dialysed for various periods, under 1 Preliminary report, Banga et al. [1939, 2].

No abstract