COMPARATIVE CHARACTERISTICS OF LIPOXYGENASE ISOENZYMES FROM GREEN PEA-SEEDS

Two electrophoretically homogeneous lipoxygenase isoenzymes (PLI and P LII) from green pea seeds were isolated by ammonium sulfate precipitat ion, gel chromatography performed under partially anaerobic conditions , and isoelectrofocusing. The pH optimum of both isoenzymes in the pre sence of 0.2% sodium cholate is pH 6.8 with linoleic acid as the subst rate. The pIs of the isoenzymes were slightly different, 6.22 +/- 0.02 6 for PLI and 5.94 +/- 0.035 for PLII. The turnover numbers were 55 se c(-1) )PLI) amd 40 sec(-1) (PLII) with linoleic acid as the substrate. PLI converts linoleic acid into 9-(61%)and 13-HPODE(4) (39%) and arac hidonic acid into 11- (27%), 5- (26%), 15- (24%), 9- (18%, 12- (4%), a nd 8-HPETE (1%) without expressed stereospecificity. Unlike PLII, PLI displays hydroperoxidase activity under anaerobic conditions. In contr ast to PLI, PLII converts linoleic acid into 13-HPODE (89%) with predo minant content of L(s)-isomer (87%). Arachidonic acid is predominantly converted by PLII into 1 5-HPETE (73%) with the predominance of the L (s)-isomer (91%).