The complete amino acid sequence of wool protein SCMKB-IIIB3 was determined. The peptides used for the sequence work were obtained by peptic and thermolysin digestions and were fractionated by chromatography on DEAE-cellulose, paper chromatography and electrophoresis. The peptides were analysed by dansyl-Edman degradation, mass spectrometry and tritium-labelling of C-terminal residues. The protein consists of 98 residues and has acetylalanine as N-terminal residue and carboxymethylcysteine as C-terminus. It is homologous with protein SCMKB-IIIB2 (Haylett & Swart, 1969). A salient feature of the sequence of protein SCMKB-IIIB3 is three consecutive cysteine residues.

The complete amino acid sequences of wool protein SCMKB-IIIA3 (131 residues) and a minor component SCMKB-IIIA3A (130 residues) have been determined. The proteins are mutually homologous and have free threonine as the N-terminal residue and carboxymethylcysteine as the C-terminus. The peptides used for the sequence work were obtained by trypsin, thermolysin, pepsin and chymotrypsin digestions and were fractionated by chromatography on DEAE-cellulose, gel filtration on Sephadex G-25 and G-50, paper chromatography and electrophoresis. The Edman degradation method (employing both the Beckman Sequencer and a non-automatic procedure) was used to obtain the sequences of the peptides.

A reinvestigation of a fraction of the high-sulfur proteins SCMKB was made. The proteins were successively fractionated on an electrophoretic, molecular-size, and chromatographic basis. This work resulted in the isolation of a homogeneous protein SCMKB-IIIB2 which has a molecular weight of 11,260, no free amino-terminal group, and contains S-carboxymethyl cysteine as carboxy-terminal residue.

The first complete amino-acid sequence of a wool protein is presented. The high-sulfur protein SCMKB-IIIB2, with a molecular weight of 11,260, consists of 97 residues and has an acetylated amino terminal. A notable feature of the protein is that it has a high- and a low-sulfur region. The sequence was determined by examination of the peptides released by various proteolytic enzymes and separated by chromatography on DEAE-cellulose with volatile buffers.

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