Studies of citric acid metabolism in heart muscle.

Our present knowledge in the metabolism of citric acid in vitro in animal tissues is derived almost entirely either from experiments with tissue preparations possessing both synthesizing and utilizing properties regarding this acid, or from experiments carried out by means of crude preparations of one or other of the enzyme systems involved in citric acid metabolism, therefore without dynamic connections with other metabolic pathways leading to the formation of citric acid. The aim of the experiments summarized in this paper has been to obtain heart muscle preparations which favour the formation of citric acid but do not utilize citric acid, so that it could accumulate in quantities sufficient to be estimated. Although some intermediate steps are still rather obscure, starting with pyruvic acid as the principal precursor of citric acid it is possible to consider two pathways of formation: