Synthetic protease inhibitors and post-ejaculatory degradation of human semen proteins

Normal post-ejaculatory proteolytic changes in human seminal plasma rapidly distort its electrophoretic protein pattern. This invalidates the electrophoretic evaluation of the content in the secretion from the accessory sex glands. Both agarose and sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) were used to study the proteolytic changes and how they could be modified by various synthetic protease inhibitors. Liquefaction of coagulated semen could be inhibited by adding o-phenanthroline directly after ejaculation, whereas neither neutrally buffered Na2EDTA, di-isopropylfluorophosphate (DFP), benzamidine, nor thiol reagents proved effective. Addition of the serine protease inhibitors DFP and benzamidine, o-phenanthroline, and iodoacetamide substantially retarded the proteolytic alterations of the proteins as demonstrated by both agarose electrophoresis and SDS-PAGE. We recommend that electrophoretic protein analysis of human semen be performed on ejaculates collected in vessels containing protease inhibitors. For routine analysis, the addition of benzamidine ensures sufficient stable proteins to permit reliable electrophoretic analysis of samples stored at room temperature for 4 h.