Phosphorylation of carbohydrates in retinal extracts

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Abstract
The presence of hexokinase in retinal extracts was demonstrated. In the presence of ATP it phosphorylates glucose, fructose, mannose and glucosamine. Mg, Mn and to a smaller extent Co activate the enzyme in dialyzed extracts. Both glucose and glucosamine inhibit the utilization of fructose, implying that all 3 sugars are substrates of a common hexokinase. Glucosamine is converted into a monophosphate derivative which is not further metabolized by the extracts; the other sugars yield fructose l:6-phosphate. Direct evidence for the presence of phosphohexose isomerase and of phosphofructokinase is also presented.