[Rayan]

Hello,

say we have this a decapeptide

glu-arg-pro-asp-met-cys-val-hist-trp-cys
                   |           |                      |
                  NH₂       |___S_____S____|

we were asked to calculate the pHi of this peptide so do we just take each amino acid alone and calculate its pHi?

we we given the Pka of alpha COOH, beta and gamma COOH, alpha NH₂, epsilon NH₂, and R of hist and arg. what does R mean?!!

[sdekivit]

i think they mean with R the restgroup of the aminoacids, thus for arginine the NH2(+)-groups and for histidine the ring structure. Thus the side chains.

Remeber the common structure of amino acids:

(+)H3N - CR - COO(-) (at physiologic pH)