Chapter 10

You have isolated a dimeric enzyme that contains two identical active sites. The binding of substrate to one active site decreases the substrate affinity of the other active site. Can the concerted model account for this negative cooperativity?

An allosteric enzyme that follows the concerted mechanism has a T/R ratio of 300 in the absence of substrate. Suppose that a mutation reversed the ratio. How would this mutation affect the relation between the rate of the reaction and substrate concentration?

The phosphorylation and dephosphorylation of proteins is a vital means of regulation. Protein kinases attach phosphoryl groups, whereas only a phosphatase will remove the phosphoryl group from the target protein. What is the energy cost of this means of covalent regulation?

Each of the three types of fibrin chains contains repeating heptapeptide units (abcdefg) in which residues \(a\) and \(d\) are hydrophobic. Propose a reason for this regularity.

The sedimenation value of aspartate transcarbamoylase decreases when the enzyme switches to the \(\mathrm{R}\) state. On the basis of the allosteric properties of the enzyme, explain why the sedimentation value decreases.

Write a mechanism (in detail) for the phosphorylation of a serine residue by ATP catalyzed by a protein kinase. What groups might you expect to find in the enzyme's active site?