You have isolated a new protease that cleaves peptide bonds following Asp and Glu. Based on its inactivation by DIPF, you suspect that it may utilize a mechanism similar to chymotrypsin. The difference in specificity might be explained by:

A. the presence of a positively charged residue in the S1 binding pocket.
B. the replacement of serine-195 with a positively charged residue.
C. the presence of a negatively charged residue in the S1 binding pocket.