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The thermophilic archaebacterium Thermoproteus tenax expresses two GAPDH enzymes: one that carries out the reaction shown in the chapter (although NADP+ is the reactant rather than NAD+) and a second GAPDH enzyme that catalyzes the reaction shown below. T. tenax GAPDH Glyceraldehyde-3-phosphate + NAD+ 3-phosphoglycerate + NADH+ H+ How do the properties of the two enzymes differ? The GAPDH enzyme presented in the chapter produces ATP; the second GAPDH enzyme does not produce ATP. The GAPDH enzyme presented in the chapter reduces NAD+; the second GAPDH enzyme reduces NADP+. The GAPDH enzyme presented in the chapter phosphorylates GAP; the second GAPDH enzyme produces 3PG. O All of the above.
In an experiment, the activity of the second T. tenax GAPDH enzyme was measured in the presence of various metabolites. The results are shown in the figure below. Estimate the KM values for the enzyme in the presence and absence of effectors. 25 20 Velocity (units .mg protein) 5 1 J 5 10 15 20 [NAD*] (MM) NADP+ + Control AMP * Glucose-1-P KM (Control) is approximately mM. KM (NADP+) is approximately mM. 3.0 0.5 5.0 1.5 KM (AMP) is approximately M. KM (G1P) is approximately 4 mm.
Using the results in the graph shown below, classify the effectors as activators or inhibitors of the enzyme. 25 20 15 Velocity (units .mg protein) 10 5 1 thie 10 5 15 20 [NAD*] (MM) Control + AMP * Glucose-1-P NADP+ NADP+ is ar AMP is an activator inhibitor G1P is an