Tricine-SDS-PAGE was performed according to a method described by Schagger and von Jagow (1987) with a slight modification. Briefly, 4% of stacking and 16% of separating gels were prepared using gel buffer (3M Tris- HCl, 0.3% SDS, pH 8.45), acrylamide/bisacrylamide (48% acrylamide, 1.5% bisacrylamide), distilled water, glycerol, ammonium persulfate and TEMED