Which three (or possibly more if you must) enzymes downstream of GALT allow for quantitative correlation of a product of GALT with the appearance of NADPH? What is the stoichiometric relationship between Galactose 1-phosphate and NADPH if all enzymes are present?
The Beutler test is used to diagnose GALT (UDP-glucose uridyltransferase) deficiency in infants. Blood from the heel is spotted onto filter paper and the spot is then subjected to an enzyme assay. Galactose 1-phosphate, NADP+ and UDP-glucose are added as substrates to the dried blood. The increase in absorbance at 340nm is measured over time which corresponds to reduction of NADP+ to NADPH . The amount of GALT activity in the blood of patients is therefore measured by stoichiometric relationship to the amount of NADPH produced from NADP+. However, GALT does not directly reduce NADP+ as you can see in the above diagram. Instead, the glucose 1-phosphate product from this reaction is shuttled into the oxidative phase of the pentose phosphate pathway by enzymes also present in RBCs. Which three (or possibly more if you must) enzymes downstream of GALT allow for quantitative correlation of a product of GALT with the appearance of NADPH? What is the stoichiometric relationship between Galactose 1-phosphate and NADPH if all enzymes are present?
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