PubMed Health⌕ Search

Biomedical subjects

A B Chetverin

Publications and source records attributed to A B Chetverin.

29 records · Page 2Linked to original sources
PubMed1985

Do sodium and potassium forms of Na,K-ATPase differ in their secondary structure?

Infrared spectroscopy in the amide I region of purified membrane-bound Na,K-ATPase preparation shows that Na+- and K+-bound forms of the enzyme have almost the same secondary structure. No difference is detected in the beta-structure (pleated sheets) content. This is contrary to the statement of the recent paper (Gresalfi, T. J., and Wallace, B. A. (1984) J. Biol. Chem. 259, 2622-2628) where a similar preparation was examined by circular dichroism spectroscopy and it was claimed that net 7% of protein peptide groups undergo a beta-sheet to alpha-helix conformational change upon Na,K-ATPase conversion from the K+ to the Na+ form. The discrepancy of the results is most likely caused by the particulate nature of the enzyme preparations used that could lead to optical artifacts in CD but not in IR measurements. A thorough comparison of IR spectra of these enzyme forms has revealed a very minor spectral difference which could suggest conformational perturbations, if any, of a much lower scale and another type than that claimed by Gresalfi and Wallace. The K+ form tends to absorb slightly more in the region of the alpha-helix band. This could reflect some distortion or a transition to a random coil structure of a small fraction of alpha-helical segments (less than or equal to 2% protein peptide groups) upon the enzyme conversion from the K+ to the Na+ form.

Animals↗
PubMed1980

Lack of gross protein structure changes in the working cycle of (Na+, K+)-dependent adenosinetriphosphatase. Evidence from infrared and intrinsic fluorescence spectroscopy data.

Infrared and tryptophan fluorescence spectra of practically all sufficiently stable functional complexes of a highly purified preparation of membrane-bound (Na+, K+)-dependent ATPase have been measured. The formation of any functional complex was not accompanied by any considerable change of either shape or position of the tryptophan fluorescence spectrum. Only in the presence of adenine nucleotides was there a small decrease of fluorescence intensity (by 5-8%), which apparently results from a change of the sample light scattering. Analysis of the results obtained leads to the conclusion that the environment of no more than one or a few tryptophan residues may differ in all the (Na+, K+)-ATPase complexes studies. A comparison of infrared protein spectra in the region of amide I band showed that at any wavenumber the differences between them did not exceed 3% of the maximum absorption. This means that no more than 3% of protein peptide groups can change their conformation upon transition between the enzyme functional states. These results, obtained by two independent techniques, allow us to conclude that even if changes of the internal protein structure occur during the working cycle of this transport system, if they have an extremely local character.

Adrenal Medulla↗
PubMed1980

Small differences in tryptophan fluorescence spectra of 'sodium' and 'potassium' forms of (Na+, K+)-dependent adenosinetriphosphatase.

A detailed comparative analysis of tryptophan fluorescence spectra of 'sodium' and 'potassium' forms of (Na+, K+)-activated ATPase was carried out. The 'potassium' form spectrum is shifted relative to that of the 'sodium' form by approximately 0.5-1 nm towards shorter wavelengths. The maximal amplitude of the difference spectrum for these forms makes up about 2% of maximal fluorescence intensity of any of the forms. The shape of the difference spectrum does not depend on the solution temperature or ionic strength. The spectral differences between the forms are reversible upon addition of a functionally opposite cation (K+ for 'sodium' form and vice versa) into the medium. The results suggest that if the differences in fluorescence spectra of the 'sodium' and 'potassium' forms of (Na+, K+)-ATPase resulted from the differences in the protein structure, they may be caused by an alteration in local environment of no more than one or two tryptophan residues.

Adrenal Medulla↗
PubMed1979

[Isolation and structural properties of membrane-bound Na+,K+- adenosine triphosphatase from pig kidney].

A technique for isolation of large amounts of homogeneous Na+, K+-ATPase lipid-protein complex from pig kindney has been developed. The purity of the preparation as determined by the protein component is 96-98%, the large to small subparticle ratio being 4 : 1. The protein and lipid parts of the preparation have approximately the same mass. The enzyme activity is 1600-1900 mcmoles of inorganic phosphate released per mg of protein per hour. The protein secondary structure in a heavy water solution has been studied by infrared spectroscopy in the region of the main amide bands. It has been shown that about 20% of the peptide groups form highly ordered alpha-helical regions and about 25% are found in the pleated sheet structure with an antiparallel packing of the chains. The regions with a regular structure are mainly located in the protein component regions, inaccessible for water and are presumably involved in the formation of the hydrophobic core of the molecule. The major part of the protein structure (approximately 55%) is non-ordered and is easily accessible for water molecules.

Animals↗
PubMedDate not supplied

[Retention of nucleic acid integrity in guanidine thiocyanate lysates of whole blood].

High-molecular-mass RNA and DNA have been shown to retain their integrity for three days at room temperature, no less than two weeks at +4 degrees C, and more than a year at -20 degrees C when whole blood samples are stored as lysates containing 4 M guanidine thiocyanate. Storage time at room temperature can be prolonged at least up to 14 days if nucleic acids were precipitated by two volumes of isopropanol. This preservation technique allows storage and transportation of samples at ambient temperature and is completely compatible with the procedure of subsequent isolation of nucleic acids.

Blood↗