High Mn2+ sensitivity of vesicular galactosyltransferase in thymus and mammary gland.

~1,4-Galactosyltransferase (EC 2.4.1.22) among many other Golgi and ER glycos ltransferases, is membrane-bound and requires Mn3+ ions for activity [ 11. activation is of interest for potential clinical control of glycosylation in viruses and tumour cells, and for control of milk lactose formation. However, solubilized galactosyltransferase requires 10-3OpM Mn2+ for half-maximal activation of this essential cation site, whereas intracellular [free Mn2+] is probably below 1pM [2,3,4]. showed that galactosyltransferase, synthesizing lactose in intact Golgi membrane vesicles permeabilized with ionophore A23187, required only 0.1-0.2pM Mn2+ for half maximal activation [5]. These concentrations of Mn2+ were buffered with chelators trimethylenediaminetetraacetate and triphosphate.