Biochemistry 6th Edition by Reginald Garrett,Charles Grisham

Exercise 10

Quantitative relationships between rate constants to calculate K m , kinetic efficiency (k cat /K m ) and V max -II
Triose phosphate isomerase catalyzes the conversion of glyceraldehyde-3-phosphate to dihydroxyacetone phosphate.
Glyceraldehyde-3-P dihydroxyaceone-P
The K m of this enzyme for its substrate glyceraldehyde-3-phosphate is 1.8 x 10 -5 M.
When [glyceraldehyde-3-phosphate] = 30 µM the rate of the reaction, v, was 82.5 µmole mL -1 sec -1.
a. What is V max for this enzyme?
b. Assuming 3 nanomoles per mL of enzyme was used in this experiment ([E total ] = 3 nanomol/mL), what is k cat for this enzyme?
c. What is the catalytic efficiency (kcat/K m ) for triose phosphate isomerase?
d. Does the value of k cat /K m reveal whether triose phosphate isomerase approaches "catalytic perfection"?
e. What determines the ultimate speed limit of an enzyme-catalyzed reaction? That is, what is it that imposes the physical limit on kinetic perfection?