The fate of oxaloacetic acid in different organs

Abstract

Muscle, liver, kidney, pancreas and brain reduce oxaloacetic acid to l-malic acid; lung, spleen. placenta, peripheral nerves, embryonal and tumor tissue do not, but decarboxy-late it to pyruvic acid, which remains unaltered. Kidney, and to a small extent liver, brain and lung, condense oxaloacetic acid and pyruvic acid to a product from which by loss of one C atom citric acid is formed. Hence the feeding of C-4-dicarboxylic or C-4-monocarboxylic acids increases urinary citric acid. In muscle, no citric acid is formed. Citric acid formation in the kidney may regulate the important tissue level of C-4-dicarboxylic acids. The enzyme hydrogenating oxaloacetic acid to l-malic acid and the transaminating enzyme were extracted from tissue by phosphate soln. and purified by fractional precipitation with ammonium sulphate; the citric acid forming complex could not be brought into soln. The gradual inactivation of the different enzymes metabolizing oxaloacetic acid was investigated on surviving minced kidney tissue. The reducing enzyme first loses its activity, then the citrogenase and finally the transaminating enzyme.