Human lens hexokinase

Abstract

Clear crystalline lenses were obtained post-mortem from human prenates, neonates, young and old adults. Senile cataracts removed surgically were also studied. The specific activity of soluble fetal lens hexokinase is equal to that of the rat lens. There is a progressive decrease in specific activity as the lens size increases. In the fetal lens cortex and nucleus there is high hexokinase activity; young adult and cataractous lens nuclei are practically devoid of hexokinase activity. The epithelium and most superficial cortex possess high hexokinase levels even in the senile cataract. There is a large amount of insoluble hexokinase in the epithelium and most superficial cortex of the senile cataract. This can be solubilized with salts and detergents. No soluble or insoluble hexokinase is found in the nucleus of the senile cataract. Starch gel electrophoresis reveals the presence of Type I and probably also Type II hexokinase in the human lens. Types I and II were definitely found in the lens of the Rhesus monkey. There is a thermolabile form (presumably Type II hexokinase) and a thermostable form (presumably Type I) of hexokinase in the human lens. Michaelis constants were measured. In the fetal lens: K M glu = 0·11 m m, K M ATP = 0·74 m m; in the senile cataract: K M glu = 0·045 m m, K M ATP = 0·385 m m. There is great similarity between the hexokinases of the rat, rabbit and human lens. Further investigation employing lenses of these experimental animals is likely to yield results relevant to the human lens.