The utilization of pyruvate and its conversion to glutamate in calf lens

Abstract

Pyruvate metabolism of intact calf lens-was studied by a lens culture procedure. Aerobic incubation of lens in presence of pyruvate did not increase the high energy phosphate level above that observed when no substrate was present. However, when glucose was added to the medium, the normal high energy phosphate content could be maintained in lens incubated not only aerobically but anaerobically as well. The results indicate that calf lens depends primarily on the Embden-Meyerhof pathway. Although the citric acid cycle is present, its contribution to the over-all energy stores appears small. Study with the variously labelled forms of pyruvate revealed some features of metabolism which are different in lens than those observed in other tissues. The oxidation of C1 of pyruvate to carbon dioxide in lens is much more rapid relative to the oxidation of the other two carbon atoms of pyruvate. The Cjl oxidation is geared to a dismutation reaction, in which one molecule is decarboxylated and another moleoule is reduced to lactate. The two carbon atoms remaining after the decarboxylation, reaction are in some way incorporated into glutamic acid. The ability of lens to synthesize glutamic acid may be related to the extremely high content of glutathione in this ocular tissue.