S-Sulfocysteine as a Source of the Sulfur Atom of Cephalosporin C

S. lignicolum acid proteinases A-1, A-2, and B (S-PI-insensitive) were examined for the structure of the active sites by the method of Nakatani using PAD as a probe. We attempted to screen for substances that release zinc(II)-PAD from the complex of zinc(II)-PAD-S-PI-insensitive acid proteinases. Angiotensin I released zinc(II)-PAD from the complex as well as from the complex of S-PI-sensitive acid proteinases. Angiotensin I is a good substrate for these enzymes regardless of S-PI-sensitivity. These results suggest that the two carboxyl groups capable of binding to zinc(II)-PAD are at the active site regions of S. lignicolum enzymes and that they are involved in their catalytic actions.