Proline‐Dehydrogenase from Pumpkin (Cucurbita moschata) Cotyledons.

A NAD specific proline‐dehydrogenase was found in pumpkin (Cucurbita moschata Poir. cv. Dickinson Field) which oxidized proline to Δ1‐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 mM and for L‐proline was 2.5 mM. At 5 mM NADP, a 40% non‐competitive inhibition of proline‐dehydrogenase was obtained, while 50 μM NADP was sufficient to induce 20% inhibition. [ABSTRACT FROM AUTHOR]