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Conditions for obtaining comparable tryptic digests of denatured, alkylated ovalbumin and S-ovalbumin have been studied. The tryptic peptides soluble at pH 4 -5 were fractionated by gel filtration in 1 % formic acid. The cystine-peptide fraction was resolved into two cystine peptides by chromatography on DEAESephadex, and by amino acid analyses these were shown to be derived from the same region in the molecule. The composition of the cystine peptides from ovalbumin and S-ovalbumin was the same. Further evidence that the disulphide cross-link is in the same position in the two proteins was obtained by comparing partial acid hydrolysates of performic-acid-oxidized cystine peptides isolated from pepsin digests.
Smith et al. (Sat,) studied this question.