A new strategy for primary structure determination of proteins: Application to bovine β‐casein

Abstract
A new approach has been developed for sequencing proteins. A radioactive label is attached specifically to the C‐terminus of the protein. The labelled molecule is subjected to varying proteolysis conditions. From the electrophoretic patterns (SDS‐PAGE) of the hydrolysates, appropriate cleavage conditions are selected, giving labelled peptides of different lengths which are purified. The labelled peptides are sequenced in order of increasing size (from 1 to n), peptide (i) being sequenced until the N‐terminal sequence of peptide (i‐1) is encountered. This approach allows the determination of a complete protein sequence with a minimal number of Edman cycles. The method was successfully applied to bovine β‐casein (209 residues) which was completely resequenced with only 239 Edman cycles.