Pyrroline-5-carboxylate reductase and proline oxidase activity in the neonatal pig

Recent evidence suggests that proline is an indispensible amino acid in the diet of the young pig. A dietary requirement may relate to the activity and developmental changes of the enzymes that synthesize and degrade proline. The activity of pyrroline-5-carboxylate (P5C) reductase (EC 1.5.1.2), which catalyzes the final step in proline synthesis, and proline oxidase (EC number not assigned), which catalyzes the initial step in proline degradation, were measured in four piglet tissues from birth through to the postweaning period. There were significant changes in the activity of P5C reductase with age, but the magnitude and direction of change were dependent upon age and tissue type. Compared to literature values for the rat [5.1-82.4 mumol/(min.g tissue)], the activity was low in the piglet [1.3-18.6 mumol/(min.g tissue)]. The activity of proline oxidase was low in the piglet [0-0.6 mumol/(min.g tissue)] compared to literature values for the rat [0-5.3 mumol/(min.g tissue)] and low compared to P5C reductase [1.3-18.6 mumol/(min.g tissue)], indicating that further decreases in the activity of proline oxidase would not provide the piglet with a mechanism for conserving proline if dietary supply were limiting.