The disappearance of pyruvic decarboxylase and α-ketoglutaric decarboxylase from pigeon muscles on thiamine-deficient diets

Abstract

In homogenates of breast muscle and heart muscle acetoin and succinic semialdehyde are final products of the anaerobic metabolism of pyruvate and α-ketoglutarate respectively. Therefore the pyruvic and α-ketoglutaric decarboxylase activities of these muscles could be measured by determining the rates of production of these compounds from pyruvate and α-ketoglutarate added to the homogenates. During thiamine deprivation both activities decreased according to the curves shown in Figs. 1 and 2. Pronounced differences exist between both kinds of muscle regarding the rates of decline of the activities as well as the activities remaining at death. The presence or absence of carbohydrate in the thiamine-free diet also has a marked influence on both phenomena. In general the α-ketoglutaric decarboxylase activity decrease less rapidly than the pyruvic decarboxylase activity. At death the pyruvic decarboxylase activity of breast muscle is much higher on the carbohydrate diet than on the fat diet, while in this regard no difference appeared to exist in heart muscle. Regarding the α-ketoglutaric decarboxylase activity at death, this is also higher on the carbohydrate diet than on the fat diet in breast muscle, while in most cases the reverse was observed in heart muscle. As compared to the normal activity of breast muscle or heart muscle the final percentage decrease of the pyruvic decarboxylase activity is always much greater than that of the α-ketoglutaric decarboxylase activity, but the former also is never completely lost. The apoenzymes are completely maintained in the muscles during most of the period of deficiency; they are only partly lost in the last stages, with the exception of the α-ketoglutaric decarboxylase on the carbohydrate diet.