Concept #1: The Catalytic Constant Kcat
Concept #2: Calculating & Interpreting Kcat
Example #1: What is the turnover number for carbonic anhydrase if Vmax = 60,000 M/s and [E]T = 0.1 M?
Practice: To calculate the turnover number of an enzyme, you need to know:
Practice: If 10 μg of an enzyme (MW = 50,000 g/mol) is added to a solution containing a [substrate] 100 times greater than the Km, it catalyzes the conversion of 75 μmol of substrate into product in 3 min. What is the enzyme’s turnover #?
a) 1.25 x 105 min-1
b) 2.5 x 104 min-1
c) 1.5 x 102 min-1
d) 3.5 x 106 min-1
Concept #3: Kcat vs. Km
Practice: Studies with mutated forms of an enzyme show that changing some active-site amino acids decrease the enzyme’s turnover number (kcat) but do not affect the K m of the reaction. What is the best interpretation of these results?
Practice: The turnover number for an enzyme is known to be 5000 min -1. From the following set of data, determine both the Km and the total amount of enzyme ET.
A) What is the Km of the enzyme?
a) 1 mM.
b) 2 mM.
c) 4 mM.
d) 1000 mM.
B) What is the total amount of enzyme?