Enzymes in ornithine-proline metabolic pathway in bovine lens

Various enzyme activities related to ornithine metabolism were studied using bovine lenses, ie, ornithine ketoacid transaminase, delta-1-pyrroline-5-carboxylate reductase, and delta-1-pyrroline-5-carboxylate dehydrogenase. Ornithine ketoacid transaminase activity was found in the lens epithelium; delta-1-pyrroline-5-carboxylate reductase activity was high in both lens epithelium and cortex plus nucleus; delta-1-pyrroline-5-carboxylate dehydrogenase activity was negligible in either lens epithelium or cortex plus nucleus. These results suggest that in the bovine lens ornithine is converted to proline by the cooperative action of ornithine ketoacid transaminase and delta-1-pyrroline-5-carboxylate reductase.