Adenosine triphosphate catabolism in bovine spermatozoa

Adenosine triphosphate metabolism in caudal epididymis bovine spermatozoa was studied. Measurements by HPLC at appropriate time intervals of the spermatozoa content of ATP and its derivatives were carried out under different experimental conditions. In the presence of 2-D-glucose, cellular ATP was transformed almost quantitatively into ADP and AMP at a rate of 2.3 nmol/min per 10⁸ cells. At the same time, ADP and AMP accumulated at a rate of 1.52 and 0.58 nmol/min per 10⁸ cells, respectively. In the first 4 min, about 50% of total ATP was degraded, the AEC of the cells dropped to non-physiological values while the content of other nucleosides did not vary significantly. Inorganic P_i content also remained unchanged. Under non-induced conditions up to 240 min, no variations of the adenylic content and of the EC value was observed. Under induced and non-induced conditions, IMP and adenosine were not detected within the spermatozoa. The lack of IMP might be ascribed either to the absence of AMP deaminase, whose activity has never been found in the spermatozoa or to the intracellular environment which down regulates the activity of the enzyme. In order to explain low levels and absence of variations of adenosine, several enzymic investigations were carried out. Adenosine kinase activity was not determined, therefore the transformation of adenosine into AMP had to be excluded. Nevertheless, enzymic activities potentially able to dephosphorylate the formed AMP are present in the spermatozoa. Our findings are indicative of the existence in the spermatozoa of acid and alkaline phosphatase and of 5′-nucleotidase membrane-derived. The effects of some intracellular conditions on both AMP and PNPP hydrolysing activities were examined. This paper indicates that the intracellular pH and the content of the adenylic nucleotides and P_i of the cell exert a negative control of the rate of hydrolysis of AMP, which might explain the lack of production and variations in the spermatozoa adenosine level.