Concept #1: The Catalytic Constant K_{cat}

Concept #2: Calculating & Interpreting K_{cat}

Example #1: What is the turnover number for carbonic anhydrase if V_{max} = 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 K_{m}, it catalyzes the conversion of 75 μmol of substrate into product in 3 min. What is the enzyme’s turnover #?

a) 1.25 x 10^{5} min^{-1}

b) 2.5 x 10^{4} min^{-1}

c) 1.5 x 10^{2} min^{-1}

d) 3.5 x 10^{6} min^{-1}

Concept #3: K_{cat} vs. K_{m}

Practice: Studies with mutated forms of an enzyme show that changing some active-site amino acids decrease the enzyme’s turnover number (k_{cat}) 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 K_{m} and the total amount of enzyme E_{T}.

A) What is the K_{m} of the enzyme?

a) 1 mM.

b) 2 mM.

c) 4 mM.

d) 1000 mM.

B) What is the total amount of enzyme?