Enzymes that utilize ATP in phosphate transfer require an alkaline earth metal (M) as the cofactor. M is:

Solution & Explanation

\textbf{Answer:} (B) Kinases require $\mathrm{Mg}{}^{2+}$ as the cofactor for ATP-dependent phosphate transfer. \textbf{Solution:} Kinases — enzymes that catalyse phosphoryl transfer from ATP — need $\mathrm{Mg}{}^{2+}$ as a cofactor. The $\mathrm{Mg}{}^{2+}$ ion complexes with the phosphate groups of ATP, neutralising charge and stabilising the transition state for phosphoryl transfer. Among the alkaline earth metals listed, $\mathrm{Mg}$ is the relevant cofactor.