Glucose metabolism in the calf lens.
Carbohydrate metabolism in lens homogenates was evaluated using uniformly labeled [14C]-glucose. Metabolites were separated using HPLC and the distribution of 14C among metabolic pathways was determined. Under the standard incubation conditions employed (pH 7.4, 37 degrees C, 5 mM glucose) 40% of the glucose consumed forms lactate. The amount of 14C found in sorbitol and alpha-glycerol phosphate is 1-2%. This pathway distribution is essentially independent of glucose concentration from 2 to 35 mM. Over this range, lactate production is relatively constant at 2-3 mumol 7 hr-1. At 35 mM glucose, sorbitol production increases to 0.182 from 0.036 mumol 7 hr-1 at 5 mM glucose. The level of ATP is clearly a very significant factor in the regulation of glycolytic rate. An increase in ATP concentration from 1 to 3 mM results in a decrease in the rate of lactate production from 2.09 to 0.404 mumol 7 hr-1. The NAD/NADH ratio is significant in the distribution between lactate and alpha-GP. An increase in the level of NADP or NADPH increases sorbitol production as well as alpha-GP production. A computer program was developed to model the experimental incubation system. The calculated results are in agreement with the experimental in showing effects of ATP and perturbations of enzyme cofactor concentrations.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D005947:Glucose / Q000378:metabolism*; D005958:Glucosephosphates / Q000378:metabolism; D005994:Glycerophosphates / Q000378:metabolism; D007700:Kinetics; D007773:Lactates / Q000378:metabolism; D007908:Lens, Crystalline / Q000378:metabolism*; D008954:Models, Biological; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D013012:Sorbitol / Q000378:metabolism
D005958:Glucosephosphates; D005994:Glycerophosphates; D007773:Lactates; D009243:NAD; D013012:Sorbitol; D009249:NADP; D000255:Adenosine Triphosphate; C029620:alpha-glycerophosphoric acid; D005947:Glucose