Zn(II), Cd(II) and Cu(II) interactions on glutathione reductase and glucose-6-phosphate dehydrogenase

Kinetic characterization of the inhibition effects of Cd(II), Cu(II) and Zn(II) on glutathione reductase (GSSGR; EC 1.6.4.2.) and glucose-6-phosphate dehydrogenase (G6PD; EC 1.1.1.49) from Saccharomyces cerevisiae was made. No inhibition effect was found with Zn(II) on these enzymatic systems. The effect of Cd(II) (up to 0.16 mM) and Cu(II) (up to 0.008 mM) on GSSGR activity is consistent with a pure competitive inhibition or an uncompetitive pattern, when the varied substrate is the oxidized glutathione or the NADPH, respectively. Only Cd(II) (up to 1.0 mM) showed an inhibition effect on G6PD system, which is consistent with a mixed-type inhibition pattern. When NADP+ changes over an extensive range of concentration, the inhibition effect shows an uncompetitive character. Furthermore, when G-6-P is the varied substrate, the character of the mixed-type inhibition is competitive.