Metabolism of the retina. II. Heterogeneity and properties of the lactic dehydrogenase of cattle retina.

It was previously shown (1) that in the cornea1 epithelium pyruvate stimulated the anaerobic oxidation of t,he C-l .of glucose. This stimulation appeared to be the result of reactions coupling the reduction of triphosphopyridme nucleotide by the dehydrogenases of the phosphogluconate oxidation pathway with the oxidation of TPNH by lactic dehydrogenase. Stimulation of the C-l oxidation of glucose has also been demonstrated in tumor cells (2) and in retina (3, 4). It was thought worthwhile to ascertain whether the TPNH activity of retinal lactic dehydrogenase is compatible with the idea that the enzyme may serve as a means of reoxidizing TPNH in the intact tissue. This report describes the TPNH and DPNH activity of retinal lactic dehydrogenase and the apparent heterogeneity of the enzyme.