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(i) in the range of 1-200-mu-M and uncompetitive inhibitors 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 interface domain (P. A. Karplus, E. F. Pai, and G. E. Schulz, Eur. J. Biochem. 178, 693-703 (1989)) of the enzyme.