Abstract
Zinc has the most diverse functions in variety of biological processes. It plays crucial roles in catalytic, structural and regulatory functions. In a catalytic function, its involvement is ubiquitous in that each of six major enzyme classes has a representative that requires zinc. Recent proteome analysis reveals that about 1000 enzymes have a motif that potentially could bind zinc. Thus, the mechanisms for the activation or regulation by zinc of these enzymes should be elucidated in more detail. In the secretory pathway, a number of enzymes are properly folded and become functional by binding to zinc. Therefore, zinc transporters localized there and involved in zinc mobilization into the lumen play important roles. Two zinc transport complexes (ZnT5/ZnT6 heterodimers and ZnT7 homo-oligomers) are known to perform the task in vertebrate cells. This paper reviews current knowledge of the activation mechanism of secretory or membrane-bound zinc enzymes, emphasizing a novel mechanism for the activation of TNAP by ZnT complexes in the early secretory pathway.
