A proteins pI is {TAIL ~ the pH} at which {HEAD ~ the protein} has no net charge 
at
A proteins pI is { TAIL ~ the pH } at which { HEAD ~ the protein } has no net charge
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH