Abstract: The activities of RuBP carboxylase/oxygenase, PEP carboxylase and glyceraldehyde-3-P dehydrogenase and three cell protective enzymes (superoxide dismutase, peroxidase and catalase) were reduced to different extents when malondialdehyde (MDA) was added to cell-free extracts of spinach leaves. The activities of RuBP carboxylase/oxygenase and glyceraldehyde-3-P de-hydrogenase were inhibited markedly at lower concentration of MDA. MDA also inhibited the activities of purified horseradish peroxidase and beef liver catalase as well. This irreversible inhibition might be prevented partially by cysteine, but not by glytathione and methionine. The peak of absorption was shifted from 245 nm to 266 nm when MDA reacted with catalase. It is suggested that the damaging effect of MDA accumulated in vivo to enzymes might cause the further dysfunction of metabolism in the cell.

Key words: Malondialdehyde, Carboxylase, Cell protective enzymes, Spinach