Interactions of the Autoxidized Products of Linoleic Acid with Enzyme Proteins

Abstract

The inactivation of the enzyme protein by the autoxidized products of linoleic acid was studied with special reference to the incorporation of the autoxidized products into the protein and the consequent damage to the amino acid residues of the protein. Inactivation of ribo-nuclease (RNase) was due to the incorporation of linoleic acid hydroperoxides (LAHPO) or their secondary products (SP). Pepsin showed a lesser degree of inactivation and incorporation with re-spect to LAHPO, but SP activated the pepsin activity. Trypsin was affected only by SP. In RNase lysine, histidine, tyrosine, methionine and cystine were the most labile amino acids to LAHPO attack, while methionine was the only amino acid which suffered damage in trypsin and pepsin. The SP caused damage of methionine, lysine and histidine in RNase, methionine, cystine and histidine in trypsin and methionine and aspartic acid in pepsin. The reactions of LAHPO were enhanced by a prooxidant, ascorbic acid (AsA), while antioxidants acted otherwise. The incorporation of SP into RNase and pepsin was enhanced by AsA while antioxidants were ineffective.