Selective Purification of Phosphoserine Peptides by Diagonal Electrophoresis

Abstract

WHEN a mixture of amino-acids and/or peptides is separated on paper by ionophoresis and a strip containing all of them is sewn to a new sheet of paper and run again by ionophoresis, under the same conditions, in a direction at right angles to the first, the amino-acids or peptides will finally lie in a diagonal line because the mobility in both dimensions is the same. If the compounds are subjected to some chemical reaction before being run for the second time, however, all those with an altered ratio of charge to mass will have a different electrophoretic mobility and so should not appear on the diagonal line. This technique has been used to identify different kinds of peptides, namely, histidine peptides of the active site of phosphoglucomutase¹, C-terminal peptides of the γ chain of human foetal haemoglobin², and disulphide bridges of chymotrypsinogen A (ref. 3). In these cases the treatments before the second ionophoretic run were, respectively, photo-oxidation, digestion with carboxipeptidase B in situ and performic acid oxidation.