Four free cysteine residues found in human IgG1 of healthy donors.

Modifications with different thiol reagents demonstrated that 28 of 32 cysteine residues of human IgG1 are involved in the formation of disulfide bonds, and four cysteines remain free. So IgG1 is a protein possessing both free SH-groups and disulfide bonds. Only one of the four SH-groups is accessible for silver or mercury ions and hydrophobic reagents, whereas the remaining three SH-groups are masked and can be revealed only after deep denaturation of the protein.

The thermal unfolding and domain structure of Na+/K+-exchanging ATPase. A scanning calorimetry study.

The thermal unfolding and domain structure of Na+/K+-ATPase from pig kidney were studied by high-sensitivity differential scanning calorimetry (HS-DSC). The excess heat capacity function of Na+/K+-ATPase displays the unfolding of three cooperative domains with midpoint transition temperatures (Td) of 320.6, 327.

Location of disulfide bonds in the Na+, K(+)-ATPase alpha subunit.

For localizing S-S bonds in the pig kidney Na+,K(+)-ATPase alpha subunit, cystine-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 cystine-containing peptides performed at cysteine residues involved successive alkylation, first with radioactive iodoacetic acid and then with ABD-F in the absence and presence of a reducing agent, respectively. Cysteinyl peptides were isolated by HPLC, their amino acid sequences determined, and two disulfide bonds: Cys452-Cys456 and Cys511-Cys549 were localized by identification of fluorescent cysteine residues.