Isolation and properties of intestinal hexokinases, fructokinase, and N-acetylglucosamine kinase.

The nonspecific hexokinases of rat intestinal epithelium were isolated by diethylaminoethyl column chromatography. The major isoenzymes of hexokinase which were found were types I and II, but, in addition, the presence of types III and IV in small amounts was suggested. The nonspecific hexokinases were clearly separated from specific fructokinase and from N-acetylglucosamine kinase, an enzyme previously believed to be absent from intestine. Guinea pig intestine differed from rat intestine in three significant ways. (a) There was a relative increase of type II hexokinase compared to type I, and there was an absence of types III and IV; (b) guinea pig type II hexokinase was more sensitive to N-acetylglucosamine inhibition than was rat type II; and (c) hexokinase specific activity of guinea pig intestine was one-third that of the rat. Of the total hexokinase activity in both guinea pig and rat intestine, 50% was in a particulate form. Triton X-100 (0.5%) could solubilize 40% of this particulate hexokinase. The apparent solubilization of particulate hexokinase by 0.9 M KC1 was counteracted by the marked inhibitory effect of KC1 on both soluble and particulate hexokinases. KC1 inhibition of hexokinase activity was proportional to KC1 concentration and partly irreversible. The hexokinases of other rat organs were also inhibited by KCl. Purified intestinal epithelial microvilli had no demonstrable hexokinase activity.