The Inhibition of Glutathione Reductase by Quinones

Fully substituted quinones including some naturally occurring oxyquinones acted as inhibitors of yeast gluta­thione reductase (EC 1.6.4.2). They were competitive, mixed or uncompetitive inhibitors for NADPH , possess­ing K in the range of 1 -200 μᴍ and uncompetitive in­ hibitors for glutathione. Rhein (4,5-dioxy-9,10-anthraquinone-2-carbonic acid) and 9,10-phenanthrenequinone were the most effective inhibitors. It is concluded that certain quinones can bind to the NADP(H)-binding site and to the heteroaromatics binding site at the inter­ face domain (P. A. Karplus, E. F. Pai, and G. E. Schulz, Eur. J. Biochem. 178, 693 -703 (1989)) of the enzyme.