Classification of serine proteases derived from steric comparisons of their active sites, part II: "Ser, His, Asp arrangements in proteolytic and nonproteolytic proteins".

The assignment of serine proteases to the families of (chymo)trypsins and subtilisins, respectively, is extended by including additional data from the Brookhaven Protein Data Bank. To better understand basic properties connected with this type of assignment the steric situation in the vicinity of the tetrad aminoacyl residues and atomic distances within the tetrads are considered. A new catalytic mechanism is suggested based on differences between tonin and kallikrein with respect to structure and reactivity of the catalytic tetrad. All protein structures available from the Brookhaven Protein Data Bank are analyzed with regard to the occurrence of Asp....His....Ser triads