Cardiolipin hydrolysis by human phospholipases A2 -: The multiple enzymatic activities of human cytosolic phospholipase A2

The ability of mammalian phospholipases A(2) (PLA(2)) to hydrolyse cardiolipin (diphosphatidylglycerol) was monitored with a fluorescent displacement assay which allows the use of natural phospholipid substrates. The mammalian enzymes used were porcine pancreatic (Group I) secretory PLA(2) (sPLA(2)), human non-pancreatic (Group II) sPLA(2) and human cytosolic PLA(2) (cPLA(2)). High activity was observed with porcine pancreas sPLA(2) whereas the human sPLA(2) demonstrated only minimal activity with this substrate. In comparison, sPLA(2) from Naja naja venom (Group I) also showed only modest activity with this substrate. Since many lipases possess PLA(1) activity, a representative enzyme from Rhizopus arrhizus was also assessed for its ability to hydrolyse cardiolipin which proved to be a good substrate for this fungal lipase. In all cases dilysocardiolipin was the major product while some monolyso intermediate was detected after chromatographic separation. Human cPLA(2) was unable to hydrolyse cardiolipin at a significant rate, however, both monolysocardiolipin and dilysocardiolipin, which are prepared by the PLA(2)-catalysed hydrolysis of cardiolipin, were good substrates providing a further example of the extensive lysophospholipase activity of this enzyme. Moreover, cardiolipin that was initially hydrolysed in situ with either excess porcine pancreatic PLA(2) or R. airhizus lipase (PLA(1)) was subsequently hydrolysed by human cPLA(2). One explanation of this result is that human cPLA(2) is able to hydrolyse both 1-acyl and 2-acyl-lysophospholipids. (C) 1998 Elsevier Science B.V.