Differentiated analysis of the secondary structure of hydrophilic and hydrophobic regions in alpha- and beta-subunits of Na+,K+-ATPase by Raman spectroscopy |
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Authors: | M F Hirshman H Wallberg-Henriksson L J Wardzala E D Horton E S Horton |
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Affiliation: | Shemyakin Institute of Bioorganic Chemistry, USSR Academy of Sciences, Moscow. |
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Abstract: | Raman spectra of active Na+,K+-ATPase from pig kidney and membrane-bound products of its two-stage trypsinolysis, including alpha-subunit hydrophobic regions as well as the intact beta-subunit and hydrophobic regions of alpha- and beta-subunits, were measured to calculate the secondary structure of hydrophilic and hydrophobic regions of the enzyme. Consequent comparison demonstrated unambiguously that (i) membrane-bound hydrophobic parts of polypeptide chains of Na+,K+-ATPase subunits are in the alpha-helical conformation; (ii) essential contents of the alpha-helix as well as beta-sheet are estimated to form the hydrophilic (mainly cytoplasmic) domain of the Na+,K+-ATPase alpha-subunit; (iii) the exoplasmic hydrophilic domain of the beta-subunit is shown to include several antiparallel beta-pleated sheets and a small amount of the alpha-helix and unordered conformations. The model of the secondary structure organization of hydrophilic domains as well as 8 hydrophobic transmembrane segments of the enzyme molecule was proposed on the basis of experimental results and predictional calculations. |
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