What are the steps that Aconitase facilitates in changing Citrate to Isocitrate? 2. What does the residue Histidene 101 do as Aconitase catalyzes the change of Citrate to Cis-aconitate ? 3. What does the residue Serine 642 do as Aconitase catalyzes the change of Citrate to Cis-aconitate

2. The mechanism of HMG-CoA reducatse enzyme activity involves several stages. For the catalytic reaction to proceed, another substrate known as NADPH, which acts as a reducing agent is required. The kinetics of enzyme activity with NADPH at non-limiting amounts of HMG-CoA in the absence or presence of compactin is shown below. a) Based on the description above, which of the six types of enzymes does HMG-CoA reductase belong to? b) What is the Km for the reaction with no inhibitor present? Do NOT forget the units. Answers can be expressed either as a fraction or in decimals. c) What happens the measured Km with increasing amounts of compactin? (select one) increases decreases does not change d) What happens to the measured Vmax with increasing amounts of compactin? (select one) increases decreases does not change e) Based on your answers above, what type of inhibitor is compactin relative to its effects on enzyme activity NADPH? with -60 -40 1/V, (nanomoles/min)-1 -20 0.2 0.18 0.16…

3. Triose-phosphate isomerase (TPI) catalyzes the movement of a single proton to interconvert dihy- droxyacetone phosphate and glyceraldehyde 3-phosphate in glycolysis and gluconeogenesis. The enzyme, a dimer of identical subunits that are 248 amino acids in humans, has no cofactors, required metal ions, or cooperativity between subunits. The enzyme is found in all tissues. The value of Kcat/KM - 9.2 x 106 sec-'M-1 is close to the rate constant expected for a diffusion-limited reaction. The mechanism of the proton transfer is illustrated in the diagram below. Glu-165 Giu-165 Glu-165 ks HR H 20,PO HO, OH His-95 His-95 His-95 (a) ing structural formulas and naming enzymes and glycolytic intermediates, the reactions of the payoff phase. Consider only anerobic glycolysis. Remember that each glucose molecule yields two mole- cules of glyceraldehyde-3-phosphate (GAP). Indicate the net yield of ATP and NADH generated through anaerobic glycolysis per glucose molecule. The reaction catalyzed by…

4. Different B-latamases employ different mechanisms in catalyzing the hydrolysis of B-lactam ring. PHCH2CONH PHCH,CONH .S H20 B-lactamase čo, Two mechanisms have been proposed as below. (Mechanism A) Asp90 Asp90 NH. Asp90 Asp90 ---O-H (Mechanism B) Asp 90 Asp 90 NH- HO. Asp 90 (a) Briefly discuss the roles that the Zn* ion plays in the first and second step of Mechanism A. (b) Discuss the different roles of Asp90 in the two mechanisms.