Surface-active phospholipase A2 in mouse spermatozoa

• Published in: Biochimica et biophysica acta Vol. 754; no. 1; pp. 44 - 50
• Main Authors: Thakkar, J.K., East, J., Seyler, D., Franson, R.C.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.11.1983
• Subjects: Acetophenones - pharmacology; Animals; Calcium; Calcium - pharmacology; Chemical Phenomena; Chemistry; Enzyme Activation - drug effects; Hydrogen-Ion Concentration; Male; Membrane fusion; Mice; Mouse; Phospholipase A2; Phospholipases - isolation & purification; Phospholipases A - antagonists & inhibitors; Phospholipases A - isolation & purification; Phospholipases A1; Phospholipases A2; Spermatozoa; Spermatozoa - enzymology; Surface Properties; Membrane fusion; Spermatozoa; Phospholipase A2; Calcium; Mouse; Hepes; EGTA
• ISSN: 0005-2760; 0006-3002; 1879-145X
• DOI: 10.1016/0005-2760(83)90080-2

The partial characterization of a calcium-dependent phospholipase A2 associated with membranes of mouse sperm is described. Intact and sonicated sperm had comparable phospholipase A2 activity which was maximal at pH 8.0 using [1-14C]oleate-labeled autoclaved Escherichia coli or 1-[1-14C]stearoyl-2-acyl-3-sn-glycero-phosphorylethanolamine as substrates. More than 90% of the activity was sedimented when the sperm sonicate was centrifuged at 100000 × g, indicating that the enzyme is almost totally membrane-associated The activity is stimulated 200% during the ionophore-induced acrosome reaction and is almost equaly distributed between plasma/outer acrosomal and inner acrosomal membrane fractions. The membrane-associated phospholipase A2 had an absolute requirement for low concentrations of Ca2+; Sr2+, Mg2+ and other divalent and monovalent cations would not substitute for Ca2+. In the presence of optimal Ca2+, zinc and gold ions inhibited the activity while Cu2+ and Cd2+ were without effect. Incubation of sperm sonicates with 1-[1-14C]stearoyl-2-acyl-3-sn-glycerophosphorylethanolamine in the presence and absence of sodium deoxycholate demonstrated the presence of phospholipase A2; and lysophospholipase activities. No phospholipase A1 activity was detectable. Indomethacin, sodium meclofenamate and mepacrine, but not dexameth sone or aspirin, inhibited the sperm phospholipase A2 activity. Preincubation with p-bromophenacyl bromide inhibited phospholipase A2, suggesting the presence of histidine at the active site. The enzyme may play an important role in the membrane fusion events in fertilization.