title: Modulation of phospholipase A2 activity associated with human sperm membranes by divalent cations and calcium antagonists.
abstract: Phospholipase A2 activity in sonicates and acid extracts of ejaculated, washed human sperm was measured using [1-14C] oleate-labeled autoclaved E. coli and 1-[1-14C] stearoyl-2-acyl-3-sn- glycerophosphorylethanolamine as substrates. Phospholipase A was optimally active at pH 7.5, was calcium-dependent, and exclusively catalyzed the release of fatty acid from the 2-position of phospholipids. The activity was membrane-associated, and was solubilized by extraction with 0.18 N H2SO4. Acid extracts of human sperm had the highest specific activity (1709 nmols /h per mg), followed by mouse, rabbit and bull, which were 105, 36 and 1.7 nmols /h per mg, respectively. para-bromophenacyl bromide inhibited human sperm phospholipase A2 activity, but mepacrine was without effect. In the presence of 1.0 mM added CaCl2, phospholipase A2 activity was inhibited by Zn2+ and Mn2+; whereas Cu2+, Cd2+, Mg2+, or Sr2+ had no effect. Zn2+ stimulated activity at low concentrations (10(-6) to 10(-8) M), and inhibited activity in a dose-dependent manner at concentrations of 10(-5) M. The extent of stimulation by low concentrations of Zn2+ was dependent on Ca2+ concentration; at 10(-7) M, Zn2+ activity was stimulated 160% with 0.5 mM CaCl2, and only 120% with 1.0 mM CaCl2. At low concentrations (10(-5) to 10(-7) M), methoxyverapamil (D600) and trifluoperazine stimulated human sperm phospholipase A2 activity, and trifluoperazine but not D600 produced almost complete inhibition between 10(-5) and 10(-4) M of the drug. The significance of human sperm phospholipase A2 activity and its modulation by Ca2+, Zn2+ and Mn2+ in the sperm acrosome reaction is discussed.
mesh_terms: D000177:Acrosome / Q000187:drug effects / Q000201:enzymology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D013075:Sperm Capacitation / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects* / Q000201:enzymology
chemical_list: D002121:Calcium Channel Blockers; D002413:Cations, Divalent; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2