Biochemical and pharmacological comparison of a cytosolic, high molecular weight phospholipase A2, human synovial fluid phospholipase A2 and CoA-independent transacylase.

We have compared biochemical and pharmacological characteristics of CoA-independent transacylase (CoA-IT) activity of microsomes from U937 cells to those of two other enzymes involved in arachidonate metabolism, a human type II low molecular weight (M(r) 14,000, LMW) PLA2 isolated from synovial fluid of patients with inflammatory joint disease and a high molecular weight (M(r) 85,000, HMW) PLA2 enzyme isolated from the cytosol of human monocytic U937 cells. Activities of HMW PLA2 and CoA-IT were reduced by treatment with acid, heat or acetonitrile but were not altered by treatment with the sulfhydryl reducing agent dithiothreitol (DTT). In contrast, the activity of LMW PLA2 enzyme was inactivated by DTT, but was insensitive to treatment with acid, heat or acetonitrile. HMW PLA2 activity decreased as NaCl concentration was increased in the assay buffer from 0 to 150 mM, unlike LMW PLA2 and CoA-IT activities, which increased as NaCl increased. Compounds that inhibit LMW PLA2 activity were examined for their effects on HMW PLA2 and CoA-IT activities. The compounds examined (nordihydroguaiaretic acid, manoalide, p-bromophenacyl bromide, arachidonic acid, gossypol, aristologic acid and a mimic of a transition state phospholipid) had different rank orders for inhibition of the three enzymes. Taken together, these data show that these three enzymes, although unpurified, can be biochemically and pharmacologically distinguished.