Aspartate aminotransferase aspat catalyzes the

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52. Aspartate aminotransferase (AspAT) catalyzes the following reaction: aspartate + a—ketoglutarate---> oxaloacetate + glutamate The AspAT enzyme has two active-site arginines, Arg 386 and Arg 292, which interact with the a-carboxylate and 13-carboxylate groups on the aspartate substrate, respectively. Investigators studied the mechanism of AspAT in more detail by constructing mutant AspAT enzymes in which either or both of the essential arginines were replaced with a lysine residue. The kinetic parameters for the wild-type (normal) enzyme and mutant enzymes are shown in the table below: Enzyme KM aspartate (mM) kcat (0) Wild-type AspAT (Arg 292 Arg 386) 4 530 Mutant AspAT (Lys 292 Arg 386) 30 180 Mutant AspAT (Arg 292 Lys 386) 9 117 Mutant AspAT (Lys 292 Lys 386) 300 0.06 Of the mutant forms which has: 1) the best turnover number and which 2) has the best catalytic efficiency? A) 1) Lys 292 Arg 386; 2) Lys 292 Arg 386 D) 1) Arg 292 Lys 386; 2) Lys 292 Arg 386 B) 1) Arg 292 Lys 386; 2) Lys 292 Lys 386 E) 1) Lys 292 Arg 386; 2) Arg 292 Lys 386 C) 1) Lys 292 Lys 386; 2) Arg 292 Lys 386 F) 1) Lys 292 Lys 386; 2) Lys 292 Lys 386 53. An enzyme has a KM of 3 mM in the absence of a competitive inhibitor in a solution of 2 mM substrate and a Vmax of 15 nM/s. What concentration of a competitive inhibitor with ICI of 3 mM is required to achieve an initial velocity of 5 nM/s? A) 0.1 mM B) 0.4 mM C) 0.7 mM D) 1.0 mM E) 1.3 mM 54. A patient suffers from premature zymogen activation, so that the pancreatic enzymes are activated in the pancreas rather than the small intestine -- causing damage to the pancreas. Which of the following would be the most effective in preventing these effects? A) chymotrypsin inhibitor B) trypsin inhibitor C) elastase inhibitor 55. Calculate AG at 37°C when Ca' ions move from the endoplasmic reticulum ([Ca 2 +] = 1 mM) to the cytosol ([Ca 2 +] = 0.1 M) at a membrane potential of -50 mV (cytosol face negative). A) -33.4 kJ/mol B) -28.6 kJ/mol C) -15.1 kJ/mol D) +28.6 kJ/mol Version 3 Page 8
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I Version 3 Page 9
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Answer Key 13.E n (C III 14. 14. A 15. B 16. C i3 17. D 53. D Version 3 Page 9
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