A ®nal volume of 1 ml of 0.2 M Trisacetate buer (pH 6.0) containing 0.1 M hydroxylamine, 5 mM CaCl2, 10 mM glutathione, and 30 mM N-carbobenzyloxy-glutaminylglycine was incubated at 37C for 10 min and then neutralized by adding an equal volume of 15% tri-neutralized by adding an equal volume of 15% trichloroacetic acid-5% FeCl3, solution.