Question

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TABLE 6-8 Enzymes for which kead/Km Is Close to the Diffusion-Controlled Limit (108 to 10º M-15-1) keat kcat/Km (M-15-1) Enzyme Substrate (s-1) Acetylcholine Acetylcholinesterase Carbonic anhydrase CO2 Catalase Crotonase Fumarase HCO3 H,02 Crotonyl-COA Fumarate Malate Benzylpenicillin 1.4 x 104 1 X 106 4 X 105 4 X 107 5.7 x 103 8 X 102 9 X 102 2.0 X 103 (M) 9 x 10-5 1.2 x 10-2 2.6 x 10-2 1.1 X 100 2 x 10-5 5 x 10-6 2.5 x 10-5 2 x 10-5 1.6 x 108 8.3 x 107 1.5 X 107 4 X 107 2.8 X 108 1.6 X 108 3.6 X 107 1 x 108 B-Lactamase Source: Fersht, A. (1999) Structure and Mechanism in Protein Science, p. 166, W. H. Freeman and Company, New York,

"Looking at table 6-8 on Enzyme Reactions from the lecture, which achieves an excellent specificity constant with a very favorable kcat (insert answer here) , which with a favorable Km (insert answer here) , and which with moderate values for each (insert answer here) ? (pick from acetyl cholinesterase, B-lactamase, and catalase)"

Question 2: "The units of Vmax are (insert answer here) and the units of Km are (insert answer here)  (pick from M, M-1, M/s, s/M s-1, M-1s-1)"

question 3: A better enzyme has a  (high / low) kcat, a  (high / low) Km, and a  (high / low) specificity constant."

Answer 1

1. Given :

Enzyme name	Kcat	Km
Acetylcholinesterase	1.4 x 104	9 x 10-5
B-lactamase	2 x 103	2 x 10-5
Catalase	4 x 107	1.1 x 100

Favourable Kcat is of Catalase

Favourable Km is of B-lactamase

With moderate value of each is acetylcholinesterase

2. Unit of Vmax is

Unit of Km is M

Unit of Vmax is M/s

3. A better enzyme has a

high kcat,

low Km

high specificity constant.