Modulation of glyceraldehyde-3-phosphate dehydrogenase inAnacystis nidulans by glutathione

Abstract

Glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13; GAPDH) from the cyanobacteriumAnacystis nidulans was activated up to five-fold by reduced glutathione (GSH) in the physiological concentration range (0.1–2 mM GSH). Non-physiological reductants, like dithiothreitol (DTT) and β-mercaptoethanol, also activated the enzyme. Oxidized glutathione (GSSG) had no effect on the cyanobacterial GAPDH but treatment with H2O2 led to a rapid, reversible deactivation of both untreated and GSH-treated enzyme preparations. GSH reversed the inhibition induced by H2O2. An oligomeric form of the enzyme (apparentMr∼440,000) was dissociated by GSH into a lower-Mr, more active enzyme form (Mr∼200,000). The enzyme was shown to obey regular Michaelis-Menten kinetics. The activation of GAPDH by GSH was associated with a decrease inKm and an increase inVmax values of the enzyme for 3-phosphoglycerate. GSH had virtually no effect on a GAPDH preparation isolated from corn chloroplasts and studied for comparison.