Proteins&Enzymes 4 Answer Questions 1 - 4 using the information in the paragraph

Question

Proteins&Enzymes 4

Answer Questions 1 - 4 using the information in the paragraph and diagram below as needed. You are investigating ways to develop targeted chemotherapeutic drugs against breast cancer. From a patient, you obtain a sample of her tumor from biopsy. Since you were trained at TTU, you know also to take a sample of normal (unaffected) breast tissue for comparison. It turns out that the protein shown in the diagram below, c-Src, is highly overexpressed in the tumor tissue, but is expressed at low levels in the normal breast sample. You remember from Cell Biology that c-Src is a tyrosine kinase involved in the stimulation of cell proliferation. That is, c-Src phosphorylates other proteins on tyrosine residues of those proteins. Interestingly, a check of the c-Src protein sequence shows the tumor and the normal proteins are identical (i.e., not mutated).
4. You now measure the enzyme kinetics for c-Src from equal amounts of tumor and normal breast tissue. Let's say you make an enzyme extract out of 100,000 tumor cells and a separate extract out of 100,000 normal cells. Assume that the cells in this case are about the same size for both the tumor and normal cells. For c-Src's protein substrate, you use a short peptide with the sequence S D Y Y Y Y D S because you know that c-Src will phosphorylate that peptide on one of its tyrosine residues. You add the same volume of enzyme extract to each assay tube but add increasing amounts of subtrate peptide. You measure the initial reaction velocity (Vo) as a function of the substrate peptide concentration. You complete two experiments, one using the tumor extract and a second using the normal tissue extract. Plotting both curves (Vo vs. substrate concentration) gives two square hyperbolic curves, so the data are consistent with standard Michaelis-Menton kinetics. Given the information in the explanatory paragraph above, how do you expect the tumor enzyme kinetics to compare to the normal tissue kinetics?


A. The tumor Km will be lower than the normal sample Km.
B. The tumor Km will be higher than the normal sample Km.
C. The tumor Vmax will be higher than the normal sample Vmax.
D. The tumor Vmax will be lower than the normal sample Vmax.
E. The tumor Km and Vmax will be about the same as that of the normal enzyme.

Explanation / Answer

E. The tumor Km and Vmax will be about the same as that of the normal enzyme

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