Cysteic acid Subject

This mixture is subjected to electrophoresis in the perpendicular direction under the same conditions as those of the first electrophoresis. Peptides that were devoid of disulfides will have the same mobility as before, and consequently all will be located on a single diagonal line. In contrast, the newly formed peptides containing cysteic acid will usually migrate differently from their parent disulfide-linked peptides and hence will lie off the diagonal. These peptides can then be isolated and sequenced, and the location of the disulfide bond can be established. 

The molar ratios of the amino-acid residues were determined after erythrocuprein was subjected to acid hydrolysis at 110°C for 20 to 96 hours. The method of Moore and Stein was used throughout (88, 89). The sulfhydryl content of human erythrocuprein was determined using the spectrophotometric assay of Boyer (90). Total half-cystine was analysed as S-carboxy methyl cysteine in acid hydrolysates (91) of reduced and alkylated erythrocuprein, or as cysteic acid in acid hydrolysates oxidized with performic acid. The data are summarized in Table 2. 

Each of the hydroxyproline-rich wall protein tryptides contains a pentapeptide of serine-(hydroxyproline)4, while most of the tryptides contain one or more galactosyl residues (85). One tryptide, which was found to contain 2 residues each of galactose and serine, was subjected to P-elimination by several different methods. The elimination procedures converted serine to alanine or cysteic acid with a concomitant release of free galactose (85). These results demonstrated the covalent attachment of a single galactosyl residue to each seryl residue in the... 

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