Diacylglycerol and alkylacylglycerol stimulate ram sperm phospholipase A2.
1. We have investigated the susceptibility of ram sperm phospholipase A2 (PLA2) to stimulation by diacyl- and alkylacylglycerols and by monoacyl- and monoalkylglycerols. 2. PLA2 activity in sonicates from ram spermatozoa was enhanced when 1-stearoyl-2-arachidonoyl-sn-glycerol, the diacylglycerol usually generated by polyphosphoinositide breakdown, was added to a radioactive phosphatidylcholine substrate; the effect was time- and Ca(2+)-dependent. 3. Both diacyl- and alkylacylglycerol considerably enhanced PLA2 activity; 1-O-hexadecyl-2-O-methyl-rac-glycerol, however, only showed slight stimulatory ability. 4. The monoradylglycerols 1-monohexadecanoyl-rac-glycerol, 2-monohexadecanoylglycerol, and 1-O-hexadecyl-sn-glycerol had very little effect on the enzyme's activity. 5. Exposure of spermatozoa to 1-oleoyl-2-acetyl-sn-glycerol (OAG) or 1-O-hexadecyl-2-acetyl-rac-glycerol (1-O-C16/2-C2), when cells were stimulated with the ionophore A23187 and Ca2+, resulted in higher PLA2 activity in sperm sonicates. Furthermore, parallel experiments showed that exocytosis was enhanced if spermatozoa were treated with A23187/Ca2+ and either OAG or 1-O-C16/2-C2. Since both diacyl- and alkylacylglycerols increased PLA2 activity and exocytosis, stimulation of PLA2 activity by these diglycerides may take place independently from protein kinase C activation.
Roldan
E R
ER
Department of Development and Signalling, AFRC Babraham Institute, Cambridge, U.K.
Martinez-Dalmau
R
R
Mollinedo
F
F
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology*; D005089:Exocytosis / Q000187:drug effects; D005989:Glycerides / Q000494:pharmacology*; D008297:Male; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D012756:Sheep; D013094:Spermatozoa / Q000187:drug effects / Q000201:enzymology*
D004075:Diglycerides; D005989:Glycerides; D000001:Calcimycin; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium