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.