The kinetic properties of arginase in sperm cells of inferile men

Abstract

Nowadays the role of NO in the development of male infertility is actively studied. Arginase (EC 3.5.3.1) is a manganese metalloenzyme which converts L-arginine to L-ornithine and urea and reciprocally regulates NO production. Although arginase activity has usually been detected in the reproductive tract, including spermatozoa, no data relating to the kinetic properties of the enzyme in ejaculated spermatozoa has been reported. This study was designed to study the kinetic parameters of arginase of spermatozoa of infertile men. Spermatozoa arginase activity was measured by determining levels of urea production. Kinetic analysis of the enzyme reaction was performed in a standard incubation system with modified physical and chemical characteristics or the respective components (the substrate concentration, Mn2+ concentration, incubation time and protein content). Pathobiochemical and kinetic properties of sperm arginase obtained from human normozoo- and pathospermic samples were compared. The maximum rate of L-arginine hydrolysis (detrermined by L-arginine) for arginase of spermatozoa obtained from men with preserved fertility was 2.0, 1.8 and 1.9 times greater than this value for oligo-, astheno- and oligoasthenozoospermic samples respectively. However, affinity constants for L-arginine was not significantly different between fertile and infertile men. The maximum rate of L-arginine hydrolysis (deretmined by Mn2+) for arginase of spermatozoa obtained from men with preserved fertility was 1.6, 1.7 and 1.7 times greater than this value for oligo-, astheno- and oligoasthenozoospermic samples respectively. However, affinity constants for Mn2+ were not significantly different between fertile and infertile men. In the whole range of time, the urea production by arginase in sperm cells obtained from oligozoospermic samples is much lower compared to value in healthy donors. The results of kinetic analysis indicate that urea production by arginase is much more intense in the control group than in patients with various forms of pathospermia. The initial (instantaneous) reaction rate of arginase reaction was lower for oligozoospermic samples compared to normozoospermic samples. It has been found that inhibition of arginase activity in sperm cells of infertile men occurs by non-competitive type and was related to marked decrease in maximum reaction rate while affinity of arginase to L-arginine and Mn2+ was unaffected.

Keywords

• arginase activity; L-arginine; enzyme inhibition; spermatozoa; pathospermia