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In the decarboxylation of pyruvic acid by yeast, the question ofan initial formation ofcarbonic acid or of carbon dioxide may be investigated by the use of carbonic anhydrase. The use of this enzyme in such investigations was first suggested by Roughton and co-workers (Meldrum & Roughton, 1933; Ferguson & Roughton, 1934; Roughton, 1935). Roughton (1935) published a diagram (Krebs & Roughton, 1934) showing the effect of the enzyme on the carbon dioxide pressure when urease acts on urea. The relation of ferment to substrate was such that the total urea-splitting occurred in a very short time. The liberation of free carbon dioxide as a primary product was shown by the rapid rise of the pressure in the manometer, followed by its slow decline (over about 10-15 min.) as carbon dioxide was taken up as HCOby the buffered medium. In the presence of a sufficient concentration of carbonic anhydrase no such initial fling and return of the carbon dioxide pressure occurs. In repeating such experiments with carboxylase the difficulty lay in obtaining a preparation strong enough to act on the pyruvate substrate with adequate rapidity. Recently, Krebs & Roughton (1948) have so far fulfilled this requirement as to obtain results showing that, for the conditions studied, carbon dioxide is mainly the primary product. In the investigation of the carboxylase action with carbonic anhydrase we used a somewhat different approach, namely strong concentrations of pyruvate, so as to produce a linear or near-linear rise of pressure over the time studied (of the order of 5 min.). Initial experiments (Conway & MacDonnell, 1945) seemed to indicate an increased carbon dioxide tension in the presence of carbonic anhydrase. These preliminary experiments were technically unsatisfactory. Also, the theoretical change of pressure arising from carbonic anhydrase would be very slight at the initial pH of 5-5. Owing, however, to the inadequate buffering this pH very rapidly changed to higher values, which appears to account for the differences found. Subsequent experiments, better controlled (see O'Malley, 1947), supported the original conclusions and an account was delayed pending further clarification. Simultaneously, Krebs (1948) and Conway & O'Malley (1948) read communications concerning the effect ofcarbonic anhydrase on decarboxylation. Krebs advanced definite proof that, under the conditions studied, carbon dioxide was a primary product (though, as judged from the evidence here given, it was not necessarily the sole primary product of the carbon dioxide system). Our results supported the conclusion that whether carbon dioxide or carbonic acid was the main primary product depended on the conditions, and we gave equations, the derivations of which are described in this paper, for the theoretical evaluation of the effect of carbonic anhydrase, assuming a linear or near-linear rate of decarboxylation, as with strong pyruvate substrate. More recently, after a study of the best theoretical conditions, using the strong pyruvate substrate, a type of experiment was designed which would appear to furnish clear-cut results, the pressure changes being compared with the theoretical figure. This type of experiment only will be described in the present account.

The effect of carbonic anhydrase on the action of yeast carboxylase