isoelectric point pl,is defined as the pH at which an amino acid has zero overall charge after summing the contributions of all the charge 。 The number of positive charge equals the number of negative charge. a.When pH<pI,the overall charge is positive b.When pH>pI,the overall charge is negative H HaN+- COOH H,N COOH HN- -C00- R R R BELOW Isoelectronic ABOVE Isoelectronic Point Isoelectronic Point Point isoelectric point • pI, is defined as the pH at which an amino acid has zero overall charge after summing the contributions of all the charge • The number of positive charge equals the number of negative charge. a. When pH<pI, the overall charge is positive b. When pH>pI, the overall charge is negative c. When pH=pI, there is no overall charge