Circular dichroism changes in galactosyltransferase upon substrate binding

Circular dichroism studies with the galactosyltransferase isolated from bovine skim milk are described. Addition of UDP-galactose to the galactosyltransferase-Mn-2+ complex causes a decrease in the negative mean residue ellipticity in the 205-220-nm range and positive increases in the 265- and 275-290-nm ellipticity. These date are consistent with the view that a conformation change involving aromatic amino acid residues occurs upon the binding of UDP-galactose to the galactosyltransferase-Mn-2+ complex. No effects in the near-ultraviolet circular dichroism spectrum were observed upon the addition of UDP or glucose to the galactosyltransferase-Mn-2+ complex.