?Wheat chloroplastic glutathione reductase activity is regulated by the combined effect of pH, NADPH and GSSG?.

LASCANO, H.R.,; GÓMEZ, L.D.; CASANO L.M., ; AND TRIPPI, V.S.

PLANT AND CELL PHYSIOLOGY

Oxford Journals

Año: 1999 vol. 40 p. 683 - 690

0032-0781

To study the mechanism of regulation of chloroplastic glutathione reductase (GR) under photooxidative conditions,GR activity, and the levels of NADPH, GSH andGSSG were measured in wheat chloroplasts under photooxidativelight. GR was extremely labile, and the concentrationsof GSH and GSSG progressively diminished inchloroplasts prepared without ascorbate. The NADPHlevel did not significantly change during photooxidativetreatment. The addition of 10 mM ascorbate to the incubationmedium prevented the decrease of GSH and GSSGand strongly protected GR activity. However, ascorbatehad no effect on NADPH-dependent inhibition of the chloroplasticGR purified from wheat leaves. We studied theeffect of NADPH, temperature, pH and GSSG on the purifiedenzyme. The inhibition by NADPH was greatly dependenton temperature and pH. NADPH inhibited GR byaround 93% up to pH 7.5, but within a range of 8.0 to 9.5the inhibition was only marginal. The pH dependence ofthe NADPH inhibitory effect could be due, at least in part,to different rates in the generation of NADPH-X, a derivativeof NADPH which inactivates several pyridin nucleotidedehydrogenases. Furthermore, the NADPH-dependentinhibition was almost completely prevented by GSSG,but not by GSH.