Changes in surface ATPase of rat spermatozoa in transit from the caput to the cauda epididymidis

Summary. Rat spermatozoa from the cauda epididymidis were found to have a lower activity of the surface ATPase than the spermatozoa from the caput region. The enzyme from spermatozoa of both regions had the same Michaelis constant (Km) for ATP of 5 \m=x\10\p=n-\4M. It was partly inhibited by ouabain and fluoride, but strongly inhibited by Cu2+, Zn2+, p-chloromercuribenzoate, 8-anilino-1-naphthalenesulphonate Triton X-100, Lubrol\p=n-\PX,urea, guanidine hydrochloride, sodium dodecyl sulphate and glycerylphosphorylcholine. The enzyme of the spermatozoa from the cauda epidi-dymidis was more sensitive to inhibition by ouabain and fluoride but less sensitive to inhibition by Cu2+ than that of the cells from the caput region. The Arrhenius plot ofthe temperature dependence of enzymatic activity varied for the cells from the caput and cauda epididymidis. The differences in the enzyme properties of spermatozoa from the two regions of the epididymis suggested that the decline in the activity during epididymal maturation may reflect changes in the lipids and sulphydryl groups of the sperm membrane