An improved method for isolation of the C-terminal fragment of proteins.

An efficient and easily realizable method for the isolation of the C-terminal fragment is described. Proteins are esterified by methanolic HCl and subsequently digested with pepsin. The peptide mixture is submitted to paper electrophoresis in pH 2.1 buffer. The identification of the C-terminal peptide is performed by preparing a guide peptide map, using pH 5.5 buffer in the second dimension. The C-terminal fragment appears as an on-diagonal spot. It can be isolated by a pH 5.5 run of the corresponding band from the first (pH 2.1) electrophoretogram. Since the C-terminal peptide is the fastest moving component, there is no need for its further purification. The expected yield is about 40%.