Thiol oxidation in the crystalline lens. I. The rate-limiting role of hexokinase in aging rat and human lenses.
Reduction of nonprotein disulfides required both glucose or glucose-6-phosphate (G6P) and nicotinamide adenine dinucleotide phosphate (NADP). However, hexokinase (HK) was found to be the rate-limiting step: the glucose-supported reduction rate was only 50% of that of G6P-supported activity. This disulfide-reducing activity seemed to decline in the aging lens. Further, the glucose-supported activity dropped substantially if HK was deactivated with diamide; the deactivation was partially reversible. HK activity in aging clear and cataractous human lenses had greatly diminished. This might explain the disproportionate decrease in glucose-supported reduction in the aging lens. The components of the disulfide-reducing mechanism in human lens were reviewed and discussed.
D000367:Age Factors; D000818:Animals; D002386:Cataract / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D005958:Glucosephosphates / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006593:Hexokinase / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007908:Lens, Crystalline / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D051381:Rats
D004220:Disulfides; D005958:Glucosephosphates; D009249:NADP; D006593:Hexokinase; D005978:Glutathione; D005947:Glucose