TGase activity was measured following the procedure described by Folk and Cole (1966a,b).A ®nal volume of 1 ml of 0.2 M Tris±acetate buer (pH 6.0) containing 0.1 M hydroxylamine, 5 mM CaCl2, 10 mM glu-tathione, and 30 mM N-carbobenzyloxy-glutaminyl-glycine was incubated at 37C for 10 min and then neutralized by adding an equal volume of 15% tri-chloroacetic acid-5% FeCl3, solution. After centrifuga-tion at 4000g for 15 min at room temperature, the supernatant was collected and its absorbance measured at 525 nm.