Zinc (Zn) has been known to be an essential element for more than a hundred years, ever since it was discovered by Raulin in 1869 to be required for the growth of Aspergillus niger.1 However, it has not been until relatively modern times that the universal importance of this metal for both human and animal health became fully appreciated.2-12 To date more than 200 zinc dependent enzymes have actually been identified in all the main biochemical pathways. It acts uniquely as a Lewis acid catalyst (an electron acceptor) in all life processes.

http://orthomolecular.org/library/jom/1995/articles/1995-v10n0304-p149.shtml