Fig. 4. Co-expression of GD and Snk results in GD autoproteolysis to generate lower molecular weight polypeptides. Western blot using anti-GD specific antisera. A GD-specific polypeptide of 72 kDa was generated when GD was expressed alone. However, when GD was expressed with either wild-type Snk zymogen or a proteolytically inactive form of Snk, two polypeptides of 44 and 48 kDa were generated. Appearance of the lower molecular weight polypeptides requires integrity of the active site serine of GD.