Modification of glucose-6-phosphate dehydrogenase by 4-hydroxy-2-nonenal. Formation of cross-linked protein that inhibits the multicatalytic protease.

Incubation of glucose-6-phosphate dehydrogenase (Glu-6-PDH) from Leuconostoc mesenteroides with the lipid peroxidation product 4-hydroxy-2-nonenal leads to the formation of cross-linked protein.This is accompanied by the appearance of protein-associated fluorescence with excitation and emission maxima of 340 and 415 nm, respectively, and with the disappearance of histidine and lysine residues.Cross-linked protein is less susceptible than native Glu-6-PDH to proteolysis by the multicatalytic protease, a multienzymic proteolytic complex involved in the intracellular degradation of damaged proteins.In addition, 4-hydroxy-2-nonenalmodified Glu-6-PDH inhibits the multicatalytic protease and can therefore prevent the efficient degradation of oxidized protein.These findings may have important implications for the accumulation of altered protein and fluorescent material in uiuo, processes that are believed to be involved in age-and disease-related impairment of cellular function.Reactive oxygen species readily interact with polyunsaturated fatty acids, often resulting in the formation of cytotoxic aldehydes such as 4-hydroxy-2-nonenal (HNE)l and malondialdehyde (for review see Ref. 1).Modification of various biomolecules by these lipid peroxidation products has been implicated in a number of degenerative diseases associated with aging (2-5) and is believed to result in the formation of fluorescent material that accumulates in a variety of postmitotic cells as they age (6-13).These results have led many to postulate a role for lipid peroxidation in the aging process.There is little direct evidence, however, primarily because the chemical nature of various modifications and the effects on cellular function are not well understood.Information on the mechanisms by which lipid peroxidation products react with biological materials is required for the development of reliable methods for detection of specific modifications in various tissue preparations.Identification of cellular targets and elucidation of the properties of modified biomolecules should provide insight into mechanisms by which these processes contribute to the pathophysiology of aging.HNE, a major product of lipid peroxidation, is significantly more reactive under physiological conditions than many other