Question: The investigators carried out kinetic studies the enzyme creatine kinase in which they measured t…

The investigators carried out kinetic
studies the enzyme creatine kinase in which they measured the
ability of a second substrate to bind once the first substrate had
bound. The data are shown in Table 15.1. Kd refers to the constant
for the binding of substrate to free enzyme and KM refers to the
constant for binding of that same substrate to the enzyme when the
other substrate is already bound to the enzyme. The results for the
wild type and two of the mutants are
shown in Table 15.1.

a. Compare the Kd and KM values for
creatine and ATP for the wild-type enzyme. What does a comparison
of the Kd and KM values tell you about the ability of each
substrate to bind to the enzyme alone? to the enzyme when the other
substrate is present?

b. Similarly, compare the Kd and KM
values for the C278G mutant enzymes. Again, what does a comparison
of the Kd and KM values tell you about the ability of each
substrate to bind to the enzyme alone? to the enzyme when the other
substrate is present?

c. Consider your answers to a and b and
consider the Vmax values for both the wild type and mutant enzymes.
Assess the role of Cys 278 in the
binding of creatine and ATP substrates to the creatine kinase
enzyme.

Table
15.1: Binding constants for phosphocreatine synthesis from
creatine and ATP (modified from Furter, et al., 1993).