Suppose that your Ph. D. mentor asks you to compare the kinetic behavior of the two recently discovered peptidase isozymes PepA and PepB. Your mentor's initial studies identified a pentapeptide substrate called Tide5 that appeared to be able to distinguish the kinetic behaviors of PepA and PepB. All they had time to tell you was this: At low Tide5 concentration, the Vo (initial velocity) of PepA was greater than PepB, but at high Tide5 concentration the reverse was true. Before you start your kinetic assays, you decide it would be wise to ponder this small bit of information. You have no numbers to work with, but does it tell you something about the relative values of Km and Vmax for PepA and PepB?
Select the statements that are consistent with the information that you were given.
1. The Vmax of both isozymes could be the same, but the Km values must be different.
2. The Vmax of PepB must be greater.
3. The ratio of Vmax/Km must be larger for PepB.
4. The Km of both isozymes could be the same, but the Vmax values must be different.
5. The Km of PepB must be higher.