Protein O-carboxylmethyltransferase in spermatozoa from normal and infertile men.

In confirmation of several reports, suspensions of normal washed human spermatozoa exposed to a nonionic detergent exhibited considerable activity of the enzyme protein O-carboxylmethyltransferase (PCM), which catalyzes the methyl esterification of carboxyl groups of dicarboxylic amino acid residues in proteins. Various methods for assay of human spermatozoal PCM levels were evaluated, and some properties of the enzyme were studied. Normal human spermatozoa appear to be devoid of other types of protein methyltransferases that catalyze N-methylations of arginyl or lysyl residues in proteins. Spermatozoal PCM levels in infertile patients with motile sperm cells tended to be somewhat higher than those of normal control subjects, especially in those instances where the spermatozoal populations contained abnormally high proportions of immature forms of spermatozoa. Although totally immotile spermatozoa obtained from certain patients exhibited very low PCM activities (as recently reported by other investigators), in this study no invariant relationship between zero motility indexes and spermatozoal PCM was observed. These results are discussed in light of various current hypotheses regarding the functions of PCM in animal cells.