Glucose-6-phosphate dehydrogenase is also found in yeast, and it catalyzes the s

Question

Glucose-6-phosphate dehydrogenase is also found in yeast, and it catalyzes the same reaction shown in Problem 47. (problem 47 diagram is the one below!) The KM for glucose-6-phosphate in yeast is 2.0 3 1025 M. The KM for NADP1 is 2.0 3 1026 M. Yeast glucose-6-phosphate dehydrogenase can be inhibited by a number of cellular agents whose KI values are listed in the following table.

Inhibitor KI (M)

Inorganic phosphate 1.0 X10^-1

Glucosamine-6-phosphate 7.2 3 1X10^-4

NADPH 2.7 X10^-5

(a) Which is the most effective inhibitor? Explain.

(b) Which inhibitor(s) is (are) likely to be completely ineffective under normal cellular conditions? Explain.

CH2OPOj NADP+ CH2OPOj OH H glucose-6- phosphate dehydrogenase OH H OH H OHH Glucose-6-phosphate 6-Phosphoglucono-8-lactone Kinetic data for the enzyme isolated from the thermophilic bacterium I. maritima are presented in the following table. Substrate KM (mM) Vmax (U-mg') Glucose-6-phosphate NADP+ NAD 0.15 0.03 12.0 20 20 6

Explanation / Answer

a) Inorganic phosphate is the most effective inhibitor as its KI value is less and as the KI value decreases inhibition increases and it is inversely proportional based on the graph.

b) Glucosamine-6-phosphate is the ineffective inhibitor aas its KI value is less. Lesser KI value will take a long time to inhibit and it is ineffective.

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