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O Jardetzky

Publications and source records attributed to O Jardetzky.

At least 91 records · Page 5Linked to original sources
PubMed1981

High-resolution nuclear magnetic resonance studies of the Lac repressor. 3. Unfolding of the Lac repressor headpiece.

At temperatures below 20 degrees C, the lac repressor headpiece (N-terminal amino acids 1--51) has a well-defined structure which is independent of ionic strength. Its unfolding with increasing temperature proceeds gradually with a characteristic transition temperature which depends on ionic strength. Unfolding has been studied by using NMR and CD. Shifts of several methyl and all of the tyrosyl resonances can be followed, allowing a detailed analysis of the temperature denaturation. At high ionic strength (1 M), the unfolding is complete at 85 degrees C, while at low ionic strength (0.01 M), it is complete by 65 degrees C. Native and partially unfolded structures are in rapid exchange during the unfolding, and the process appears completely reversible at all ionic strengths.

Circular Dichroism↗
PubMed1980

Small-angle X-ray studies of the quaternary structure of the lac repressor from Escherichia coli.

The quarternary structures of the lac repressor molecule from Escherichia coli and its tetrametic core, which can be derived from it by proteolytic cleavage, were studied in dilute solutions by small-angle X-ray scattering. The dimensions and general shape of the lac repressor and of the tetrameric core are reported. The core itself appears to be an elongated structure, and in the intact repressor the headpieces are located at its ends. The results ar derived from model calculations and from the following molecular parameters determined from the scattering curve and the pair distance distribution function: for lac repressor, radius of gyration 5.30 +/- 0.02 nm, radius of gyration of the cross section 2.20 +/- 0.03 nm, maximum diameter 18.0 +/- 0.5 nm, hydrated volume 329 +/- 20 nm3, relative molecular mass 149 000 +/- 15 000, for tetrameric core, radius of gyration 4.92 +/- 0.02 nm, radius of gyration of the cross section 2.24 +/- 0.03 nm, maximum diameter 16.0 +/- 0.5 nm, hydrated volume 278 +/- 15 nm3, relative molecular mass 120 000 +/- 10 000.

Escherichia coli↗
PubMed1980

Internal motions in deoxyribonucleic acid II.

We have measured the 1H, 31P, and 13C NMR parameters of monodisperse deoxyribonucleic acid (DMA) fragments 260 and 140 base pairs long as a function of temperature and solvent viscosity. On the basis of these measurements, we calculate that within a rodlike DNA helix, the base planes, the deoxyribose sugar, and the sugar-phosphate backbone all experience large fast internal motions. The best fit of the data to a two-state model for internal motion specifies for the internal motions the following amplitudes A and correlation times tau: for the base planes, A = +/-20 degrees and tau = 1 X 10(-9) s; for position 2' of the deoxyribose sugar, A = +/-20 to +/-33 degrees and tau = 1 X 10(-9) s; for the P-H vectors of the sugar-phosphate backbone, A = +/-27 degrees and tau = 2.2 X 10(-9) s.

Animals↗
PubMed1980

Effect of ethidium bromide on deoxyribonucleic acid internal motions.

We have used 31P and 1H NMR to show that DNA internal motions are stopped or greatly hindered when ethidium bromide intercalates into DNA. We show that the effect is localized to a 2 base pair long DNA region at the binding site and that internal motions outside the binding site are nearly unaffected. Based upon the nearly independent behavior of bound and free DNA regions, we conclude that in B-DNA individual base pairs experience internal motion which is independent of the motion of their neighbors.

Animals↗
PubMed1980

On the nature of molecular conformations inferred from high-resolution NMR.

The basic, usually unstated, premises underlying the derivation of "average" conformations of flexible molecules from high-resolution NMR parameters (shifts, coupling constants and relaxation times) are critically examined. It is shown that in cases where the individual conformers contributing to the average are not known the "average" derived from spectroscopic data represents a virtual structure devoid of physical meaning.

Magnetic Resonance Spectroscopy↗
PubMed1979

Internal motions in myosin.

High-resolution proton nuclear magnetic resonance (1H NMR) measurements were made on myosin, heavy meromyosin (HMM), myosin subfragment 1 (S1), light meromyosin (LMM), and actin. A strong signal from amino acid side chains undergoing motions too fast to be accounted for by simple rotations of groups on a rigid backbone was obtained from myosin. Comparison of myosin, HMM, S1, and LMM showed that the mobile region is located almost entirely in S1 and accounts for approximately 22% of its structure. Adenosine triphosphate (ATP) and ATP analogues had no measurable effect on the S1 spectrum. Actin, on the other hand, quenched the internal motions of S1. When S1 was titrated with actin, an association was obtained which was in agreement with other measured values. The actin effect was reversed by adding magnesium pyrophosphate (MgPPi) or adenyl-5'-yl imidophosphate (MgAMPPNP). Quantitative treatment of the broad signals from myosin and its subfragments substantiated the existence of two flexible regions in myosin. The highly mobile portion of myosin may be located in the "swivel" between S1 and the rest of myosin or in the actin binding site or in both. These possibilites are discussed, and a new possible mechanism for muscle cross bridge elasticity is proposed.

Actins↗
PubMed1979

Internal motions in DNA.

We have measured the 31P and 1H NMR parameters of fractionated double-stranded DNA fragments 600, 300, and 150 base pairs long. The results indicate that, inside an intact double helix, both the deoxyribose and the sugar-phosphate backbone of the helix fluctuate substantially from their equilibrium geometry. The time constant for those coupled motions is of the order of 1 nsec.

DNA↗
PubMed1976

13C nuclear magnetic resonance study of molecular motions and conformational transitions in muscle calcium binding parvalbumins.

13C nuclear magnetic resonance is used to detect the Ca2+ ion controlled conformational transition in muscle calcium binding parvalbumin and to study its intramolecular motions. Nuclear relaxation parameters are used to evaluate the reorientation rates of the protein and some of the amino acid side chains. While peripheral residues exhibit greater motional freedom than the protein interior, an interesting finding is that significant rapid internal motion is present in the phenylalanine rings comprising the hydrophobic core of the protein.

Amino Acids↗
PubMed1976

Phosphorus-31 Fourier transform nuclear magnetic resonance study of mononucleotides and dinucleotides. 1. Chemical shifts.

A phosphorus-31 nuclear magnetic resonance (NMR) study of adenine, uracil, and thymine mononucleotides, their cyclic analogues, and the corresponding dinucleotides is reported. From the pH dependence of phosphate chemical shifts, pKa values of 6.25-6.30 are found for all 5'-mononucleotides secondary phosphate ionization, independently from the nature of the base and the presence of a hydroxyl group at the 2' position. Conversely, substitution of a hydrogen atom for a 2'-OH lowers the pKa of 3'-monoribonucleotides from 6.25 down to 5.71-5.85. This indication of a strong influence of the 2'-hydroxyl group on the 3'-phosphate is confirmed by the existence of a 0.4 to 0.5 ppm downfield shift induced by the 2'-OH on the phosphate resonance of 3'-monoribonucleotides, and 3',5'-cyclic nucleotides and dinucleotides with respect to the deoxyribosyl analogues. Phosphate chemical shifts and titration curves are affected by the ionization and the type of the base. Typically, deviations from the theoretical Henderson-Hasselbalch plots are observed upon base titration. In addition, purine displays a more deshielding influence than pyrimidine on the phosphate groups of most of the mononucleotides (0.10 to 0.25 ppm downfield shift) with a reverse situation for dinucleotides. These effects together with the importance of stereochemical arrangement (furanose ring pucker, furanose-phosphate backbone conformation, O-P-O bond angle) on the phosphate chemical shifts are discussed.

Fourier Analysis↗