Chapter 7, Problem 18P

Each gram of mammalian skeletal muscle consumes ATP at a rate of about 1 × 10-3 mol/min during contraction. To bridge the short interval between the moderate demand for ATP met by aerobic metabolism and the high demand met by anaerobic ATP production, muscles carry a small reserve of the compound creatine phosphate which, due to its high phosphoryl group transfer potential (see Figure 3.7), is capable of phosphorylating ADP very efficiently. The reaction is catalyzed by the enzyme creatine kinase:

Because the equilibrium lies well to the right, virtually all of the muscle ADP or AMP is converted to ATP as long as creatine phosphate is available. Concentrations of ATP and creatine phosphate in muscle are about 4 mM and 25 mM, respectively, and the density of muscle tissue can be taken to be about 1.2 g/ cm³.
a. How long could contraction continue using ATP alone?
b. If all creatine phosphate were converted into ATP and utilized as well, how long could contraction continue?
c. What do these answers tell you about the role of ATP in providing energy to cells?