Linoleoyl lysophosphatidylcholine is an efficient substrate for soybean lipoxygenase-1

Oxygenation of 1-linoleoyl lysophosphatidylcholine (linoleoyl-lysoPC) by soybean lipoxygenase-1 was monitored by measuring the increase of absorbance at 234nm. In support of this, the hydroperoxy derivative of linoleoyl-lysoPC as a major product and its reduction product as a minor one were detected by LC/MS analyses. The greater part of the hydroperoxy derivative was found to contain hydroperoxide group at C-13 rather than C-9, consistent with the position specificity of soybean lipoxygenase-1 in oxygenation of linoleic acid. Such a preferential production of 13-hydroperoxy derivative of linoleoyl-lysoPC was also observed at pH 7.4, suggesting that the positional specificity of lipoxygenase-1 is not affected greatly by pH. In addition, the pH-dependent oxygenation of linoleoyl-lysoPC, showing an optimal activity around pH 9, was similar to that of linoleic acid. In kinetic study, lipoxygenase 1-catalyzed oxygenation of linoleoyl-lysoPC followed Michaelis-Menten kinetics (V(m), 167.5U/mg protein; K(m), 12.9muM). In comparison, linoleoyl-lysoPC was no less efficient than linoleic acid as a substrate of soybean lipoxygenase-1. Moreover, oxygenation of linoleoyl-lysoPC by LOX-1 was not affected by detergent. Thus, linoleoyl-lysoPC could be utilized as a convenient substrate in the assay of soybean lipoxygeanse-1.