Question

why doesn't myoglobin bind well to DEAE at ph 5 even it should all be in coo- form (in ion exchange chromatography)

Answer 1

The pKa of carboxyl’s are usually between 2 and 4 depending on the environment. Therefore at pH 5 they all should be in the carboxylate form (COO-). According to the definition of the pI, it is the pH where amino group will start losing its positive charge but below pI this positive charge is in effect. This positive charge is responsible for the fact that myoglobin does not bind well with DEAE at pH 5. However, after pI point, there is only negative charge of carboxyl group so one can see binding of myoglobin with DEAE get increased.