The Crystal Structure of an Acid Protease from Rhizopus Chinensis at 2.5 a Resolution

Abstract
The acid-protease from Rhizopus chinensis was first isolated by Fukumoto, Tsuru, and Yamamoto (1). Its optimum pH for catalytic activity was shown to be between 2.9 and 3.3 (1). Although its complete sequence has not yet been determined, some limited sequence data are available — particularly that of the 39 amino-terminal residues (2,3) and of the residues in the immediate vicinity of the catalytically active aspartic acid residues (4,5). These data show that this enzyme has substantial sequence homology with porcine pepsin. Investigations of the kinetics of catalysis (6,7) have led to proposals of an extended subsite specificity.