Factors influencing pyrroline 5-carboxylate synthesis from glutamate by rat intestinal mucosa mitochondria

Factors influencing pyrroline 5-carboxylate (P5C) synthesis from glutamate by a subcellular fraction enriched in mitochondria of rat small intestinal mucosa have been studied. P5C synthesis decreased rapidly if this subcellular fraction was preincubated at 20 °C in the absence of substrates; this effect suggests that the enzyme(s) catalyzing P5C synthesis from glutamate (P5C synthase) is unstable in the absence of substrates. In the presence of substrates P5C synthesis increased linearly for the first 30 min of incubation, suggesting that the substrates promote enzyme stability. Pyridoxal 5′-phosphate is an effective inhibitor of P5C synthase whereas pyridoxamine 5′-phosphate and pyridoxal are not inhibitory. Potassium phosphate, KCl and KBr each inhibited P5C synthase but potassium-Hepes (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) did not. Potassium phosphate was the most potent inhibitor followed by KBr and then KCl. These results suggest P5C synthase is sensitive to anion inhibition. Both l-ornithine and d-ornithine inhibited P5C synthase; l-proline did not inhibit. Several analogs of ornithine and proline were also tested and none was found to inhibit P5C synthase; the inhibition by ornithine is, therefore, rather specific and it may prove to contribute to the regulation of metabolism of these amino acids.