Approaches to Disulfide Bonds Identification in the Na⁺/K⁺-ATPase Alpha Subunit

Abstract

Na⁺/K⁺-ATPase is known to be a thiol-dependent enzyme (1,2). Available data indicate to the presence of essential SH groups in the enzyme active site (10). Disulfide bonds have been identified and their reduction was shown to lead to inactivation of the enzyme (7,8). The Na⁺/K⁺-ATPase beta subunit was found to contain 3 disulfide bonds (8,9), while their number in the alpha subunit of the enzyme is still the subject of discussion. Evidently, the discrepancy in the reported results be due to the presence in Na⁺/K⁺ -ATPase of a large number of masked SH groups, which complicates differentiating them from true cysteine residues involved in the formation of disulfide bonds (3). For understanding of the domain organization of the catalytic subunit, localization of S-S bonds in the polypeptide chain is of prime significance and therefore has been chosen as a focus of our present investigations.