The investigators next carried out kinetic studies in which they measured the ab
ID: 31854 • Letter: T
Question
The investigators next carried out kinetic studies 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 two 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 4a and 4b 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.
Enzyme
Creatine
ATP
Vmax, ?mol/min
Kd, mM
KM, mM
Kd, mM
KM, mM
Wild-type
19.6
8.9
0.70
0.32
60.7
C278G
64
273
0.27
1.13
6.0
C278S
92
209
0.31
0.70
2.0
Enzyme
Creatine
ATP
Vmax, ?mol/min
Kd, mM
KM, mM
Kd, mM
KM, mM
Wild-type
19.6
8.9
0.70
0.32
60.7
C278G
64
273
0.27
1.13
6.0
C278S
92
209
0.31
0.70
2.0
Explanation / Answer
A biocatalyst catalyzes all most all types of biological reactions in a cell and it is called an enzyme. A typical human or plant or bacterial cell has different types of enzymes, for example the cellular digestive enzymes found in lysosomes, ATP (adenosine triphosphate) synthesizing enzyme and fatty acid degradation enzymes are found in mitochondria and peroxisomes. Every enzyme has specificity and binding constant (Kd) and Km for its substrate.
a)
According to the given data, based on the comparison of Kd and KM values for creatine and ATP for the wild-type enzyme tells about tells about the ability of each substrate to bind to the enzyme when the other substrate is present.
b)
According to the given data, based on the comparison of Kd and KM values for creatine and ATP for the wo mutant enzymes tells about tells about the ability of each substrate to bind to the enzyme alone.
c)
Based on the given Vmax (velocity maximum) values, the role of Cys 278 in wild type is providing proper enzymatic action. Whereas, in both mutants exhibit the competitive inhibition.
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