Kinetic properties of hexokinase of germ cells in rat testis

The Michaelis-Menten constants (Km) of glucose, fructose, galactose, 2-deoxy-D-glucose and ATP as substrate for hexokinase of spermatocyte, spermatid and cauda epididymal spermatozoa extracts were measured. The Km value of glucose was very similar for all three germ cells. It was also true for all other substrates. The affinity of glucose for this enzyme was the highest while that of fructose was the lowest. The Km values were in general agreement with characteristics of hexokinase extracted from other tissues of rat. The Vmax values were also determined. The Vmax ratio of fructose to glucose showed the highest values of 1.1. The Vmax ratios of other substrates to glucose were below 1.0. The results suggest that hexokinase in the germ cells is similar to that in other tissues in its kinetic properties.