EFFECT OF HIGH PHYSIOLOGICAL TEMPERATURES ON NAD- APPARENT INHIBITIONOF GLYCINE OXIDATION( CONTENT OF GREEN LEAF MITOCHONDRIA )

We observed a rapid decline in the rate of glycine oxidation by purifi ed pea (Pisum sativum L.) leaf mitochondria preincubated at 40-degrees -C for 2 min. In contrast, exogenous NADH and succinate oxidations wer e not affected by the heat treatment. We first demonstrated that the i nhibition of glycine oxidation was not attributable to a direct effect of high temperatures on glycine decarboxylase/serine hydroxymethyltra nsferase. We observed that (a) addition of NAD+ to the incubation medi um resulted in a resumption of glycine-dependent O2 uptake by intact m itochondria, (b) addition of NAD+ to the suspending medium prevented t he decline in the rate of glycine-dependent O2 consumption by pea leaf mitochondria incubated at 40-degrees-C, (c) NAD+ concentration in the matrix space collapses within only 5 min of warm temperature treatmen t, and (d) mitochondria treated with the NAD+ analog N-4-azido-2-nitro phenyl-4-aminobutyryl-3'-NAD+ retained high rates of glycine-dependent O2 uptake after preincubation at 40-degrees-C. Therefore, we conclude that the massive and rapid efflux of NAD+, leading to the apparent in hibition of glycine oxidation, occurs through the specific NAD+ carrie r present in the inner membrane of plant mitochondria. Finally, our da ta provide further evidence that NAD+ is not firmly bound to the inner membrane.