KINETIC PROPERTIES OF NO-SYNTHASE OF SPERMATOZOA OF INFERTILE MEN
Introduction. Nitrogen (II) oxide (NO) is a highly reactive molecule involved in the regulation of numerous biochemical processes and physiological functions. The role of NO/NO-synthase of spermatozoa in the NO/NOS system of sperm cells in male infertility is widely studied. Previously, we found redistribution of activities in the NO-synthase system with their shift toward Ca2+-independent inducible isoform, which indicates dismetabolic changes in NO synthesis, namely its hyperproduction. However, it is unclear which biochemical mechanisms cause a disturbance of functional activity of NOS.
The aim of the study – to learn the kinetic properties of NOS isoforms of spermatozoa in fertile and infertile men with different forms of pathospermia.
Research Methods. Studies were conducted on sperm cells from men who had undergone a primary examination related to infertility. The WHO criteria (2010) were used in this work to assess morphological characteristics of spermatozoa. The NOS activity was determined by the formation of L-citrulline by a highly specific method of color reaction with antipyrine. The study of the kinetic properties of NOS was carried out in a standard incubation medium that was modified by substrate concentration. The imaginary kinetic parameters characterizing the NOS reaction were calculated in the Lineweaver-Burk plot.
Results and Discussion. The value of the initial maximum activity of cNOS in the spermatozoa of asthenozoospermic men was 1.5 fold (р<0.001) lower than this value in fertile men with normozoospermia. At the same time, there was no statistically significant difference in the value of the initial maximal activity of the enzyme between the normo- and oligozoospermic samples. The value of the apparent affinity constant of cNOS to L-arginine in spermatozoa from infertile men was 1.6–2.7 fold higher than that in normozoospermic men, indicating a decrease in the affinity of enzyme to L-arginine in pathospermic men. The value of the initial maximal activity of iNOS in pathospermic men exceeds this value for cNOS in 1.7–2.3 fold.
Conclusions. The obtained results indicate that in case of oligozoospermy the inhibition of cNOS activity is due to the increase in enzyme affinity to the substrate. In the case of asthenozoospermia the inhibition of cNOS activity is due to the decrease of the enzyme affinity to the substrate and decrease in enzyme rate.
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