Affinities of various mammalian arachidonate lipoxygenases and cyclooxygenases for molecular oxygen as substrate

In an attempt to study affinities for molecular oxygen of mammalian arachid onate oxygenases, which remain unclarified at present, we determined activi ties of platelet-type 12-lipoxygenase, leukocyte-type 12-lipoxygenase, 5-li poxygenase, 15-ljpoxygenase, cyclooxygenase-1 and cyclooxygenase-2 at vario us oxygen concentrations. Activities of all the tested enzymes were assesse d by oxygenation of radioactive arachidonic acid under hypoxic conditions, and part of the enzymes were also assayed by monitoring oxygen consumption. Their K-m values for oxygen ranged between 10 and 26 mu M. These results s hould be considered in investigations of arachidonic acid metabolism in pat hophysiological processes associated with hypoxia. (C) 1999 Elsevier Scienc e B.V. All rights reserved.