Is ATP a substrate for 15-lipoxygenase?

Lipoxygenases catalyze peroxidation of polyunsaturated fatty acids containi ng the 1-cis, 4-cis pentadiene structure. Linoleic (18:2), linolenic (18:3) , and arachidonic (20:4) acids are the predominant substrates for this clas s of enzymes. Effects of 15-lipoxygenase on the hydrolysis of adenosine 5'- triphosphate were investigated in vitro using soybean lipoxygenase and aden osine 5'-[gamma-P-32]triphosphate. The amount of inorganic phosphate releas ed from adenosine 5'-triphosphate was dependent upon enzyme as well as subs trate concentrations, pH, and the duration of incubation. The ATPase activi ty with a V-max value of 3.3 mu mol.mg protein(-1).h(-1) and a K-m value of 5.9 mM was noted in the presence of different concentrations of ATP at pH = 7.4. Phenidone, a lipoxygenase inhibitor, had no effect on this reaction. These findings suggest that soybean lipoxygenase catalyzes the release of inorganic phosphate from ATP primarily via hydrolysis.