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].
