Isolation, structure and protein composition of the perforatorium of rat spermatozoa

Heads of spermatozoa were sonically separated from tails and treated in 1 N NaOH until the perforatoria were partially detached from the nucleus. Their complete detachment was then assured by repeatedly passing the suspension through a 22-gauge needle. The perforatoria were then separated from nuclei on sucrose gradients and the purity of the fraction was verified by electron microscopy. The isolated perforatoria were denatured and used to raise antibodies or run on polycrylamide gels. Such gels revealed many polypeptide bands, six of which were most prominent (Mr approximately 13,000, 13,400, 16,000, 33,000, 35,000, and 43,000). Of these, the 16,000 Mr polypeptide was major. Anti-perforatorium serum reacted with the perforatoria of fixed spermatozoa, with a substance found between the plasmalemma and the outer acrosomal membrane of the acrosomal head cap and with the inner component of the ventral spur, but not with the postacrosomal dense lamina. This observation indicated that the perforatorium and dense lamina, although structurally continuous to form the perinuclear theca, are biochemically distinct. On Western blots, the anti-perforatorium serum reacted with the prominent polypeptides of the perforatorium and cross-reacted with some less prominent polypeptides of the fibrous sheath (FS) and outer dense fibers (ODF), most notably with a 16,000 Mr polypeptide found in both. Likewise anti-FS or anti-ODF serum cross-reacted with some major and minor polypeptides of the perforatorium, again most notably with a major 16,000 Mr polypeptide. The immunocross-reactions observed on Western blots were confirmed by immunocytochemical methods applied to spermatozoa. These results demonstrate that the perforatorium is composed of several polypeptides, is immunologically distinct from the postacrosomal dense lamina, may be immunologically similar to a substance found between the plasmalemma and outer acrosomal membrane and to a substance found on the inner aspect of the ventral spur, has antigenic determinants in common with the FS and ODF, and may share a 16,000 Mr polypeptide with these two cytoskeletal structures of the flagellum.