Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites, whereas protein phosphatases catalyze removal of phosphate(s)from phosphorylated proteins. Phosphorylation and dephosphorylation can function as an on-off switch for a protein's activity, most likely through
A) the change in a protein's charge leading to a conformational change. B) the change in a protein's charge leading to cleavage. C) a change in the optimal pH at which a reaction will occur. D) a change in the optimal temperature at which a reaction will occur. E) the excision of one or more peptides.