A Unique Role of Histidine in Fe-Catalyzed Lipid Oxidation by Fish Sarcoplasmic Reticulum
The sarcoplasmic reticulum (SR) fraction of fish muscle contains an enzymic lipid peroxidation system requiring NADH and Fe that is stimulated by ADP.1,2 Although in these and other studies, concentrations of metabolites used are representative of the conditions in situ, the amount of Fe is present at a much higher concentration than would normally occur in tissues, e.g., Fe in the low molecular weight fraction of flounder muscle is <3% of total iron.3 Thus, the amount and state of the Fe is most probably a rate limiting factor in lipid oxidation in situ. A large number of 0- N-, and S-containing compounds are capable of binding Fe in either the Fe+2 or Fe+3 states, and it is likely, therefore, that Fe is not found free in vivo but is bound to these cellular metabolites. Chelation of Fe is important in lipid oxidation in vitro since it may keep the Fe soluble or change its oxidation-reduction potential. In this study, we demonstrate that the free amino acid histidine can either enhance or inhibit Fe-catalyzed lipid oxidation to a significant degree. The effect of histidine is determined in part by the presence of a nucleotide.
KeywordsSarcoplasmic Reticulum Lipid Oxidation Lipid Peroxidative Activity Sarcoplasmic Reticulum Protein Ascorbate Ferrous
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