Biochemistry 4th Edition by Reginald Garrett, Charles Grisham

Exercise 8

Estimate the quantitative effects of allosteric regulators on glycogen phosphorylase activity.
Enzymes have evolved such that their K m values (or K 0.5 values) for substrate(s) are roughly equal to the in vivo concentration(s) of the substrate(s). Assume that glycogen phosphorylase is assayed at [P i ] K 0.5 in the absence and presence of AMP or ATP. Estimate from Figure 15.15 the relative glycogen phosphorylase activity when (a) neither AMP or ATP is present, (b) AMP is present, and (c) ATP is present. (Hint: Use a ruler to get relative values for the velocity v at the appropriate midpoints of the saturation curves.)