Zinc is a cofactor of

Metalloenzymes: These enzymes hold the metals rather tightly which are not readily exchanged.  Alcohol dehydrogenase, carbonic anhydrase, alkaline phosphatase, carboxypeptidase and aldolase contain zinc. Phenol oxidase (copper); Pyruvate oxidase (manganese); Xanthine oxidase (molybdenum); Cytochrome oxidase (iron and copper). Satyanrayana, Ed 3, page no 91