The addition of increasing amounts of EDTA to the reaction mixtures greatly reduced the enzymic activity. In the presence of calcium ions, however, ATPase activities were sustained, but when the concentration of the added EDTA was increased to that of calcium the enzymic activity was significantly reduced; the resulting reduction in ATPase activity was ascribed to the chelating properties of EDTA.

Determination of the enzyme and protein distribution in the head, mid-piece, tail, and an unidentified lighter fraction of testicular and ejaculated spermatozoa revealed that cation-dependent ATPase activities were lowest in the heads although the fractions accounted for more than 42% of the total protein. With the exception of the mid-piece of testicular spermatozoa, which possessed only 18% of the total enzymic activity, ATPase activities were about equally distributed in the remaining fractions and were always less in testicular than in ejaculated spermatozoa. The implications of these findings with respect to differences in motility between testicular and ejaculated spermatozoa have been considered.