Reversibly catalyzes the synthesis and degradation of trehalose from glucose and alpha-D-glucose 1-phosphate. The equilibrium lies in the direction of trehalose synthesis. alpha,alpha-trehalose + phosphate = alpha-D-glucose + alpha-D-glucose 1-phosphate Activity abolished by 1 mM Cu(2+). 0.1 mM Cu(2+) reduces trehalose phosphorolysis to 76% and trehalose synthesis to 48% of maximum activity. 1 mM Zn(2+) abolishes trehalose synthesis, and reduces trehalose phosphorolysis to 40% of maximum activity. Unaffected by EDTA. Optimum pH is 6.5 for trehalose phosphorolysis activity, 6.5-6.8 for trehalose synthesis activity. Optimum temperature is 32.5 degrees Celsius for trehalose phosphorolysis activity, 37.5 degrees Celsius for trehalose synthesis activity. Stable up to 35 degrees Celsius for trehalose phosphorolysis activity, 32.5 degrees Celsius for trehalose synthesis activity. Homodimer. Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 4 subfamily.