Z. Huang et al., A CONTINUOUS FLUORESCENCE-BASED ASSAY FOR THE HUMAN HIGH-MOLECULAR-WEIGHT CYTOSOLIC PHOSPHOLIPASE A(2), Analytical biochemistry, 222(1), 1994, pp. 110-115
A sensitive method for continuously monitoring the activity of the hum
an cytosolic phospholipase A(2) (cPLA(2)) is described. Recombinant cP
LA(2) efficiently hydrolyzes fatty acid esters of 7-hydroxycoumarin, p
roducing the free fatty acid and the highly fluorescent 7-hydroxycouma
rin. All of the observed 7-hydroxycoumarinyl ester hydrolase activity
(7-HCEase) in a preparation of the purified recombinant cPLA(2) was du
e to this enzyme since: (1) all of the ester hydrolase activity comigr
ated on nondenaturing polyacrylamide gel with a protein characterized
as the cPLA(2) by Western analysis; (2) the immunoreactive protein als
o possessed both phospholipase A(2) and lysophospholipase activities;
and (3) arachidonyl trifluoromethyl ketone, a potent inhibitor of the
phospholipase A(2) activity of cPLA(2), also inhibited the 7-HCEase ac
tivity. A study of the 7-HCEase activity demonstrated that when 7-hydr
oxycoumarinyl gamma-linolenate was dispersed in a phospholipid matrix
it was hydrolyzed by cPLA(2) at a rate comparable to that of an arachi
donyl-containing phospholipid substrate and with an identical reaction
progress curve. In the presence of phospholipid vesicles, the cPLA(2)
-catalyzed hydrolysis of hydrophobic 7-hydroxycoumarinyl esters was st
imulated by submicromolar concentration of free calcium and showed a p
reference for polyunsaturated substrates. The cPLA(2)-catalyzed hydrol
ysis of the water-soluble substrate 7-hydroxycoumarinyl 6-heptenoate w
as catalyzed by cPLA(2) in the absence of calcium and other lipids. (C
) 1994 Academic Press, Inc.