Enolase, an enzyme that catalyzes the conversion of 2-phosphoglycerate to phosphoenol- pyruvate: demonstrates a base-catalysis step, where a proton is removed from the substrate. demonstrates an acid-catalysis step, where a proton is added to the substrate. requires two Mg2+ cofactors and as such demonstrates metal-ion catalysis. stabilizes the intermediate and transition state via non-covalent interactions supplied by both the enzyme and the metal-ions. does all of the above..