Which one of the following is correct? I. All enzymes are highly specific for the reactions they catalyze. II. Prosthetic groups are loosely associated with the polypeptide chain of an enzyme. III. If an enzyme-catalyzed reaction requires a group with a low pK to be deprotonated and a group with a higher pK to be protonated, the pH vs. rate curve will have a peak in the middle of the two pK values. IV. When comparing types of catalysis, the proximity effect provides the largest rate enhancement.