A high activity carbonic anhydrase isoenzyme (CA II) is present in mammalian spermatozoa.

Human and rat spermatozoa were stained for different carbonic anhydrase (CA) isoenzymes using specific antisera to human CA I, II and VI in conjunction with the immunofluorescence technique. The spermatozoa of both species were found to contain only CA II, which was located principally in the postacrosomal region of the human spermatozoa and in the acrosomal cap region of the rat spermatozoa. The presence of CA II could be confirmed by immunoblotting, which revealed a 29 K polypeptide in both the human and rat spermatozoa. No CA I or VI-specific fluorescence could be detected in the spermatozoa of either species. The immunoblottings were also negative. The results show mammalian spermatozoa to contain the high activity carbonic anhydrase isoenzyme II. Its presence is probably linked to hydration of CO2 produced by active energy metabolism and thereby to the maintaining of an adequate intraspermatozoal bicarbonate concentration as required for the maintenance of sperm motility.