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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 amino acid sequence of the N-terminal 48 residues of the heavy chain derived from a homogeneous rabbit antibody to type III pneumococci is described. This chain of allotype a(2) is compared with other rabbit heavy chains of allotypes a(1), a(2) and a(3). Within the N-terminal 25 positions, two chains which carry the same allotype a(2) possess identical amino acid sequences, but differ markedly from heavy chains of allotypes a(1) and a(3). Sequence variability is observed in residues 26-27 and 30-34, but not in residues 35-48.

1. The selective isolation of an `active' histidine peptide from reduced and cyanoethylated chymotrypsin-α inhibited with Tos-Phe-CH2Cl (l-1-tosylamido-2-phenylethyl chloromethyl ketone) was obtained with a His(τCm) (Nτ-carboxymethylhistidine) diagonal peptide-mapπng'technique.Performicacapours,usedbetweenthefirstandseconddimensionsofthediagonalpeptmapπng′technique.Performicacapours,usedbetweenthefirstandseconddimensionsofthediagonalpeptmap', resulted in a peracid rearrangement of the alkylated (Tos-Phe-CH2)-histidine-57 residue into an Nτ-carboxymethylhistidine residue. The consequent change in electrophoretic mobility allowed isolation of peptides that contained the `active' histidine. 2. Peptides containing methionine or S-cyanoethylcysteine were oxidized to their sulphones during the treatment. Peptides in which these residues were N-terminal were selectively isolated on the basis of the change in electrophoretic mobility at pH6.5 which was due to the depression of the pK of the terminal amino group by the inductive effect of the sulphonyl group. 3. An attempt to apply the method to subtilisin BPN′ inhibited with l-1-benzyloxycarbonylamido-2-phenylethyl bromomethyl ketone failed to yield a peptide containing Nτ-carboxymethylhistidine, although peptides containing N-terminal methionine were isolated by the procedure.

Three type K Bence-Jones proteins have been fully reduced and carboxymethylated with high-specific-activity iodo[14C]acetate. A tryptic digest and a chymotryptic digest of each protein were fractionated on a Sephadex column and the radioactive peptides were purified by paper electrophoresis. All the proteins studied had five unique carboxymethylated cysteine sequences. Three of these were identical with the exception of a single substitution, and two had some variations. The common peptides could be placed in the C-terminal half of the molecule. The variations around the other two half-cysteine residues provided information about the nature of the variability of the primary sequence of immunoglobulin κ-chains. The results are consistent with the hypothesis that the chains derive from a common ancestor by somatic mutation of a small number of genes or by gene doubling and selection in the course of evolution. The isolation of the N-terminal peptide in methionine-containing Bence-Jones proteins is also described.