devil_nick Posted January 11, 2013 Share Posted January 11, 2013 At a pH below their pI, proteins carry a net positive charge; above their pI they carry a net negative charge. ( information from Wikipedia) why is this happen?? Can anyone explains the theory?? If talk about glutamine acid?? Link to comment Share on other sites More sharing options...
BabcockHall Posted January 24, 2013 Share Posted January 24, 2013 Consider a solution of glutamate at its pI (which I seem to recall is about 3.25). At this pH, the ammonium group has a one full (+) charge. The side chain carboxylic acid is mostly neutral, but a small percentage of the time it loses a proton. Therefore it has roughly a charge of 0.1(-). The carboxylic acid that is directly attached to the alpha carbon has a charge of roughly 0.9(-). Thus the positive and negative charges cancel out at this pH. These numbers all depend on one's choice of pKa values. Link to comment Share on other sites More sharing options...
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