Pyrroline-5-carboxylate reductase in human erythrocytes.

Pyrroline-5-carboxylate reductase, which converts pyrroline-5-carboxylate to proline, has been identified in human erythrocytes. The level of pyrroline-5-carboxylate reductase activity in these cells is comparable to the activity levels of major erythrocyte enzymes. The physiologic function of the enzyme in erythrocytes cannot be related to its function in other tissues, i.e., producing proline for protein synthesis. We examined the kinetic properties of erythrocyte pyrroline-5-carboxylate reductase and compared them to the properties of the enzyme from proliferating cultured human fibroblasts. We found that the kinetic properties and regulation of the erythrocyte enzyme are distinctly different from those for human fibroblast pyrroline-5-carboxylate reductase. These characteristics are consistent with the interpretation that the function of the enzyme in human erythrocytes may be to generate oxidizing potential in the form of NADP+.