Question

Glutamic acid has pKas at 2.19, 4.25 and 9.67 for the alpha-carboxyl group, side chain, and alpha-amino group, respectively. Calculate the isoelectric point for glutamic acid. You may use the provided scrap paper to perform the calculation

Answer 1

we had acidic amino acid i.e 2COOH and 1NH2 group, isolelectric point is where +ve charge of NH3+ and negative charge of COO- is balanced , under acidic conditions NH2 exists as NH3+ i.e we had now +1 charge , we need -1 charge on whole by two acidici COOH , hence we take average of pkas of two COOH so that at that pH we have overlall COO- equal to NH3+

For acidic amino acid pI = (pka1 + pka2 ) /2

hence pI ( 2.19 + 4.25) /2 = 3.22

hence isolectric point is 3.22