Amino Acid Sequences Containing Half-Cystine Residues in Ovalbumin

Abstract

Ovalbumin is known to have 6 half-cystine residues with 4 thiol groups and 1 disulfide bond. Peptides containing the 6 half-cystine residues labeled with [2-14C]iodoacetic acid were isolated from pepsin digests of reduced and S-carboxymethylated ovalbumin by gel filtration, paper ionophoresis and paper chromatography. The peptides were analyzed for amino acids and sequenced by the dansyl-Edman procedure. Cysteic acid peptides selectively recovered from enzyme digests of performic acid-oxidized ovalbumin were used to confirm some sequences. The amino acid sequences around the 2 half-cystine residues involved in the disulfide bond were determined on cysteic acid peptides. These were derived from the disulfide-containing peptide of S-carboxymethylated ovalbumin after pepsin digestion and fractionation by gel filtration, ionophoresis at pH 1.8, performic acid oxidation and another ionophoresis by the diagonal technique.