The Sequence of Sheep κ‐Casein: Primary Structure of para‐κA‐Casein

The primary structure of sheep para‐xA‐casein, the N‐terminal portion of x‐casein, was established. The reduced alkylated protein was subjected to digestion with trypsin. The resulting soluble peptides were purified by a combination of Dowex 1 × 2 chromatography and electrophoresis and chromatography on paper; the core peptides were solubilized in 50% formic acid and filtered on Sephadex G‐50. The amino‐acid sequence of these peptides was determined chiefly with a Sequencer. Alignment of the tryptic peptides into a single chain containing 105 amino acids was determined from basic overlap peptides (tryptic core peptides with several basic amino acids; chymotryptic peptides). Some comparisons were achieved with cow para‐xA‐Casein.