Triglyceride lipase activity in rhesus monkey spermatozoa.

Abstract

This study reports the presence of triglyceride (TG) lipase activity in monkey spermatozoa. Sperm sonicates catalyzed the hydrolysis of [14C]triolein to [14C]oleic acid at a rate of approximately 180 nmoles fatty acid/h · 109 sperm. The rate of fatty acid release was linear with time and sperm concentration. The apparent Km of TG lipase in sperm sonicates was 3 mM triolein. Subcellular fractionation of sperm sonicates showed 59, 21, and 14% of the total cellular activity associated with a l00,000g soluble fraction, a 3000g pellet, and a 300g head fraction, respectively. Since monkey spermatozoa contain adenylate cyclase, cyclic adenosine 3′,5′-monophosphate (cAMP), cAMP phosphodiesterase, and cAMP-dependent protein kinase, and since cAMP or its analogs stimulate sperm respiration, glycolysis, and motility, the role of cAMP in sperm lipolysis was studied. The following data indicate the apparent absence of a cAMP-stimulable lipase activity in monkey spermatozoa. (1) Under conditions which inactivate hormone-sensitive lipase in adipose tissue, lipase activity in sperm sonicates did not decrease, in spite of a reduction in endogenous cAMP content from 61 to 9 pmoles per 109 cells and a reduction in intracellular ATP content from 250 to 2.5 nmoles per 109 cells. (2) No stimulation of lipase activity was observed in either intact or sonically disrupted sperm preparations after incubation with theophylline or N6,O2′-dibutyryl adenosine 3′,5′-monophosphate (DBcAMP). Moreover, no stimulation of lipolysis in sperm sonicates was observed after the addition of cAMP, magnesium acetate, and ATP, or an ATP-regenerating system. (3) A highly purified inhibitor of cAMP-dependent protein kinase, obtained from rabbit muscle, at concentrations which completely inhibit protein kinase activity in sperm sonicates, failed to inhibit sperm lipase activity. These results suggest that sperm triglyceride lipase activity, in contrast to the hormone-sensitive lipase in adipose tissue, is not regulated by cAMP-dependent protein phosphorylations.