INACTIVATION OF GLUTATHIONE-REDUCTASE BY 4-HYDROXYNONENAL AND OTHER ENDOGENOUS ALDEHYDES

4-Hydroxynonenal, a product of oxidative degradation of unsaturated li pids, is an endogenous reactive alpha,beta-unsaturated aldehyde with n umerous biological activities. 4-Hydroxynonenal rapidly inactivated gl utathione reductase in an NADPH-dependent reaction. Inactivation appea rs to involve the initial formation of an enzyme-inactivator complex, K-D = 0.5 mu M, followed by the inactivation reaction, k = 1.3 x 10(-2 ) min.(-1). alpha,beta-Unsaturated aldehydes such as acrolein, crotona ldehyde, and cinnamaldehyde also inactivated glutathione reductase, al though rates varied widely. Inactivation of glutathione reductase by a lpha,beta-unsaturated aldehydes was followed by slower NADPH-independe nt reactions that led to formation of nonfluorescent cross-linked prod ucts, accompanied by loss of lysine and histidine residues. Other reac tive endogenous aldehydes such as methylglyoxal, 3-deoxyglucosone, and xylosone inactivated glutathione reductase by an NADPH-independent me chanism, with methylglyoxal being the most reactive. However, 2-oxoald ehydes were much less effective than 4-hydroxynonenal. Inactivation of glutathione reductase by these 2-oxoaldehydes was followed by slower reactions that led to the formation of fluorescent cross-linked produc ts over a period of several weeks. These changes were accompanied by l oss of arginine residues. Thus, the sequence of events is different fo r inactivation and modification of glutathione reductase by alpha,beta -unsaturated aldehydes compared with 2-oxoaldehydes with respect to ki netics, NADPH requirements, fluorescence changes, and loss of amino ac id residues. The ability of 4-hydroxynonenal at low concentrations to inactivate glutathione reductase, a central antioxidant enzyme, sugges ts that oxidative degradation of unsaturated lipids may initiate a pos itive feedback loop that enhances the potential for oxidative damage. (C) 1997 Elsevier Science Inc.