ANALYSIS OF DISULFIDE-CONTAINING FRAGMENTS OF N+,K+-ATPASE .3. AMINO-ACID-SEQUENCE OF CYSTEINYL PEPTIDES, LOCATION OF DISULFIDE BONDS OF ALPHA-SUBUNIT

For localization of S-S bonds in the pig kidney Na+,K+-ATPase alpha-subunit, cysteine-containing peptides (V-1, VII-1, and VII-2) obtained in our previous study from the enzyme's tryptic digest were analysed. Chemical modification of the cysteine - containing peptides performed by cysteine residues involved successive alkylations with radioactive iodoacetic acid and with ABD-F in the absence and presence of a reducing agent, respectively. Cysteinyl peptides were isolated by HPLC, their amino acid sequences were determined, and two disulfide bonds, Cys(452) - Cys(456) and Cys(511) - Cys(549), were localized by identification of fluorescent cysteine residues.