Enzymes metabolizing Δ1-pyrroline-5-carboxylate in rat tissues

Abstract

The direction and capacity for the metabolism of .DELTA.1-pyrroline-5-carboxylate in a number of rat tissues were investigated by measuring the activities of .DELTA.1-pyrroline-5-carboxylate reductase [EC 1.5.1.2], .DELTA.1-pyrroline-5-carboxylate dehydrogenase [EC 1.5.1.12] and proline oxidase. Each of these enzymes catalyzed unidirectional reactions in which .DELTA.1-pyrroline-5-carboxylate was either the substrate or product. .DELTA.1-Pyrroline-5-carboxylate reductase activities that were much higher than any previously reported were obtained by avoiding its inactivation in the cold. .DELTA.1-Pyrroline-5-carboxylate dehydrogenase, previously said to act on both D- and L-isomers of .DELTA.1-pyrroline-5-carboxylate, acted only on the L-isomer. Proline oxidase could not be measured in 2 adult tissues, in which an inhibitor appeared after birth. The activity of .DELTA.1-pyrroline-5-carboxylate reductase significantly paralleled that of ornithine aminotransferase [EC 2.6.1.13] in 23 tissues, showing a widespread potential for proline synthesis from ornithine. An independently distributed potential in fewer tissues for proline degradation to .alpha.-oxoglutarate was shown by the significantly similar tissue distributions of proline oxidase. .DELTA.1-pyrroline-5-carboxylate dehydrogenase and glutamate dehydrogenase [EC 1.4.1.2]. Reverse metabolism of glutamate or proline to ornithine would be atypical in rat tissues with these distributions of unidirectional enzyme reactions.