Synthesizes trehalose from ADP-glucose and glucose. The reaction is reversible, the equilibrium strongly favors trehalose synthesis. an NDP-alpha-D-glucose + D-glucose = a ribonucleoside 5'-diphosphate + alpha,alpha-trehalose + H(+) Inhibited by 20 mM Fe(3+) and Mn(2+). Partially inhibited by Zn(2+) and Ni(2+). Activity is slightly enhanced by 2 mM Fe (3+), Mn (2+), Ca(2+) or Li(+) and by 20 mM Mg(2+), Ca(2+) or Li(+). Optimum pH is 8.0-10.0. Optimum temperature is 60 degrees Celsius. Active between 20 and 80 degrees Celsius. Half-life at 60 degrees Celsius is 309 hours. Half-life at 70 degrees Celsius is 4.1 hours. Homodimer. Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 4 subfamily.