OXIDATION OF LINOLEIC-ACID AND METHYL LINOLEATE BY POTATO AND SOYBEANLIPOXYGENASES - A COMPARATIVE-STUDY

The role of the substrate carboxyl group in the oxidation of fatty aci ds by potato 5-lipoxygenase and soybean 15-lipoxygenase has been studi ed. Esterification of the carboxyl does not change the affinity of the substrate to 5-lipoxygenase and the pH dependencies with the modified substrate are not altered for either lipoxygenase. Esterification of the carboxyl group of linoleic acid increases significantly (4-5-fold) the lag period for 5-lipoxygenase activation and the steady-state rat e for this reaction decreases 3-fold. The lag period can be reduced by addition of 10(-4)M sodium phosphatidate, sodium n-dodecyl phosphonat e, sodium n-dodecyl sulfate, and some aliphatic carboxylic acids. Unde r these conditions, the steady-state rate of the reaction increases 3- fold. The rate of linoleic acid oxidation by 15-lipoxygenase in the re gion of pH optimum of enzymatic action does not change in the presence of the above mentioned compounds. It is concluded that the enzymes sh ould be assigned to different classes of lipoxygenases differing in th e structure of their active sites.