Question $4.$ Acyl carrier protein $($ACP$)$ is a chaperone protein for transport of fatty acids covalently attached via a covalent thioester linkage to a phosphopantetheine cofactor on ACP. As illustrated in the above scheme, cleavage of the fatty acid from ACP can be catalyzed using two different reaction mechanisms: $(1)$ general nucleophilic thioester hydrolysis $(x=$ any nucleophile$)$ and $(2)$ general base catalyzed thioester

hydrolysis $(x=$ hydroxide$).$

A$.$ Apply the steady$-$state approximation to the tetrahedral intermediate and derive an expression for $k_{\frac{?}{abs}}$ for each reaction pathway.

B$.$ Propose an experiment to discriminate reaction mechanism $(1)$ from $(2).$