Proline‐Dehydrogenase from Pumpkin (<i>Cucurbita moschata</i>) Cotyledons

Abstract

Abstract A NAD specific proline‐dehydrogenase was found in pumpkin ( Cucurbita moschata Poir. cv. Dickinson Field) which oxidized proline to Δ 1 ‐pyrroline‐5‐carboxylate. NADP did not substitute for NAD and L‐proline‐methyl‐ester and thiazolidine‐4‐carboxylate were substrates in the reaction, at a rate of 107% and 33% respectively, of the rate with L‐proline. Pumpkin cotyledons contained the bulk of the enzyme activity with 90% of the activity being in the soluble fraction. Proline‐dehydrogenase, which was not treated at high temperature, was stable at –10°C for 4 months in the presence of high ammonium sulfate concentration. The Michaelis constant for NAD was 2.2 m M and for L‐proline was 2.5 m M . At 5 m M NADP, a 40% non‐competitive inhibition of proline‐dehydrogenase was obtained, while 50 μ M NADP was sufficient to induce 20% inhibition.