Comparison of the catalytic and structural properties of Ca2+-ATPase in longitudinal tubules and terminal cisternae of the sarcoplasmic reticulum

The catalytic behavior and structural features of Ca2+-ATPase in the vesicles of longitudinal tubules and terminal cisternae of the sarcoplasmic reticulum isolated from rabbit skeletal muscles was analysed. pH measurements have shown under optimal conditions Ca2+-ATPase has similar catalytic behavior both in the fractions of longitudinal tubules and terminal cisternae. Under non-optimal conditions, the behavior similarity was not observed. The specific activity of the ATPase enzyme under optimal conditions was shown to be much higher in the fraction of longitudinal tubules than in the fraction of terminal cisternae. Caffeine added to both fractions had no effect on the catalytic behavior of Ca2+-ATPase. As judged from fluorescence analysis, the structure of Ca2+-ATPase of longitudinal tubules differs from that structure of terminal cisternae. In sarcoplasmic reticulum membrane, at least half of the tryptophan residues of Ca2+-ATPase was shown to be buried in the lipid bilayer. Our findings suggest that in terminal cisternae some of the Ca2+-ATPase molecules exist as an oligomeric protein and do not participate in ATP hydrolysis (named "silent" Ca2+-ATPase).     

Energy of interaction in actinomycin-nucleotide complexes

Complexes of the natural heterocyclic antibiotic actinomycin D (AMD) with its putative carriers: purine and pyrimidine nucleotides, as well as with fragmented DNA and phospholipid liposomes have been studied by high-sensitivity spectrophotometry. The antibiotic is not only adsorbed onto the surface of purine clusters but also is incorporated into them. It is especially readily incorporated into unwound DNA regions. The incorporation is accompanied by a long-wavelength shift of the absorption spectrum. From the magnitude of the shift, the energy of interaction was calculated. In the case of AMD in the complex with caffeine and adenosine, it is 2.4 and 2.7 kcal/mol, and in the complex with guanosine and fragmented DNA it is considerably higher, 3.3 and 3.7 kcal/mol. It is assumed that guanosine, adenosine, caffeine and fragmented DNA may serve as carriers of the antibiotic.     

Hydrophobic core malleability of a de novo designed three-helix bundle protein

De novo protein design provides a tool for testing the principles that stabilize the structures of proteins. Recently, we described the design and structure determination of alpha(3)D, a three-helix bundle protein with a well-packed hydrophobic core. Here, we test the malleability and adaptability of this protein's structure by mutating a small, Ala residue (A60) in its core to larger, hydrophobic side-chains, Leu and Ile. Such changes introduce strain into the structures of natural proteins, and therefore generally destabilize the native state. By contrast, these mutations were slightly stabilizing ( approximately 1.5 kcal mol(-1)) to the tertiary structure of alpha(3)D. The value of DeltaC(p) for unfolding of these mutants was not greatly affected relative to wild-type, indicating that the change in solvent accessibility for unfolding was similar. However, two-dimensional heteronuclear single quantum coherence spectra indicate that the protein adjusts to the introduction of steric bulk in different ways. A60L-alpha(3)D showed serious erosion in the dispersion of both the amide backbone as well as the side-chain methyl chemical shifts. By contrast, A60I-alpha(3)D showed excellent dispersion of the backbone resonances, and selective changes in dispersion of the aliphatic side-chains proximal to the site of mutation. Together, these data suggest that alpha(3)D, although folded into a unique three-dimensional structure, is nevertheless more malleable and flexible than most natural, native proteins.     

Response to remarks of S. S. Kolesnikov on the conduct of screening hypochromism

The remarks of S.S. Kolesnikov regarding the screening hypochromism are considered in the order of their citation.     

Non stacking binding of 7-amino-actinomycin D and actinomycin D to DNA and model nucleotide systems in solutions

Mechanism of actinomycin D (AMD) and 7-aminoactinomycin D (7AAMD) interaction with DNA and model nucleotide compounds was studied by absorption and fluorescence spectroscopy (steady-state, phase-modulation, and polarization). It was shown that complex formation does not result in energy transfer from photoexcited nucleotides to phenoxazone chromophore of 7AAMD that indicates the absence of stacking-like intercalation. This fact is fundamentally important to explain the biological effect of actinomycin on cells. It was revealed a fundamental difference in the complex-forming properties of AMD and 7AAMD. Thus AMD is capable of binding to guanine micelles to destroy them. 7AAMD forms complexes neither guanine micelles nor polyguanilic acid. 7AAMD binding sites on DNA can differ substantially from AMD binding sites. However, a strong competition is observed between AMD and 7AAMD for binding site in oligonucleotide HP1 used as DNA hairpin model. The efficient diameters of 7AAMD-HP1 complex and free 7AAMD were determined using the Levshin-Perren equation.     

Thermo- and photoinduced aggregation of alpha-crystallin

Some properties of bovine alpha-crystallin, in particular its thermo- and photoaggregation, were studied by fluorescent spectroscopy of tryptophan residues and the probe 8-anilino-1-naphthalenesulfonate and light scattering. The effective diameter of a globule of native alpha-crystallin was 90 A, as estimated from the data on the polarization and lifetime of 8-anilino-1-naphthalenesulfonate using the Levshin-Perren equation, and increases at an aggregation of no less than 140 A. The increase in the intensity of tryptophan fluorescence of alpha-crystallin during its thermo- and photodenaturation with the formation of aggregates is due to local conformational changes in the surroundings of tryptophan residues and light scattering. Tryptophan residues are buried in the interior of the aggregates. The thermoaggregation of the protein occurs not only at high temperatures. By approximating the experimental time dependence of slow spontaneous aggregation to the range of large times, the time of denaturation aggregation t(e) was found. For alpha-crystallin (at a concentration of 0.8 mg/ml in phosphate buffer at pH 8.4), t(e) at 70 degrees C is 100 h. This approach can be used in finding t(e) for any protein during its thermal treatment or long-term storage.     

Rotenone-insensitive NADH oxydation in mitochondrial suspension occurs by NADH dehydrogenase of respiratory chain fragments

Two types of NADH oxidation, rotenone-sensitive and rotenone-insensitive, in suspension of beef heart mitochondria were investigated by the spectrophotometric method. The oxidation of the added NADH by mitochondria in hypotonic media occurs only through the NADH dehydrogenase of the respiratory chain, since it was totally blocked by rotenone or amytal (and also by antimycin A or azide), but the ferricyanide-activated NADH oxidation was insensitive to these inhibitors. The insensitivity of the NADH dehydrogenase to rotenone appears to be due to a shunt of the electron transfer to ferricyanide without involving of ubiquinone. Both types of the oxydation occur through one and the same enzyme, which exists in two states. The evidence in favour of this is that NAD+ and DTT slightly influence the first type of oxidation but strongly inhibit the second one. The ferricyanide-activated NADH oxidation takes place in NADH dehydrogenase fragments released from mitochondria. Low Ds-Na concentrations block the respiratory chain NADH oxidation but increase the velocity of the ferricyanide-dependent oxidation. Probably, the increase is the result of the detergent-induced additional releasing of the fragments. The express-method for the preparation of the initially purified fraction with a high yield of detergent-containing fragments of the active enzyme is described.     

Nonstacking Binding of 7-Aminoactinomycin D and Actinomycin D to DNA and Model Nucleotide Systems in Solutions

The mechanism of actinomycin D (AMD) and 7-aminoactinomycin D (7AAMD) interaction with DNA and model nucleotide compounds was studied by absorption and fluorescence spectroscopy (steady-state, phase-modulation, and polarization). It was shown that complex formation does not result in energy transfer from photoexcited nucleotides to the phenoxazone chromophore of 7AAMD, which indicates the absence of stacking-like intercalation. This fact is fundamentally important to explain the biological effect of actinomycin on cells. A basic difference was revealed in the complex-forming properties of AMD and 7AAMD. Thus AMD is capable of binding to guanine micelles to destroy them; 7AAMD forms no complexes with either guanine micelles or polyguanylic acid. 7AAMD binding sites on DNA can differ substantially from AMD binding sites. However, strong competition is observed between AMD and 7AAMD for the binding site in oligonucleotide HP1 used as a DNA hairpin model. The effective diameters of 7AAMD–HP1 complex and free 7AAMD were determined using the Levshin–Perren equation.