[tjalfe89]

why is it that proteases do not cleave their own peptide bonds? - i thought it might had something to do with the structural conformation of the enzyme, so that it owns peptide residues would not fit in the pocket?

Trypsin and chymotrypsin do not cleave a peptide bond as long the next residue is proline, why is that? - i thought it maybe could be that proline make conformational changes because its a secondary amid so the residue of interest would no longer fit in the pocket. ..or maybe it have something to do with proline not able to make hydrogen bonds?

and my last question: I got a enzyme with highest activity at pH = 7. which of the following pairs of aminoacids would be candidates for catalytic groups?

glutamic acid and lysine
aspartic acid and histidine
histidine and cysteine
histidine and histidine
histidine and lysine

i know it have something to with pI values, but i cant quite figure this out.