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B T Nall

Publications and source records attributed to B T Nall.

40 records · Page 3Linked to original sources
PubMed1981

Structural studies of A-form sodium deoxyribonucleic acid: phosphorus-31 nuclear magnetic resonance of oriented fibers.

A highly oriented sample of A-form sodium deoxyribonucleic acid (DNA) has been investigated by using proton-enhanced 31P nuclear magnetic resonance (NMR). Proton-decoupled spectra taken with different angles between the magnetic field direction and the fiber direction are compared to theoretical spectra which are calculated by assuming the following: (1) the orientation of the phosphate groups in the fiber is given by the A-form DNA coordinates suggested by Arnott & Hukins [Arnott, S., & Hukins, D. W. L. (1972) Biochem. Biophys. Res. Commun. 47, 1504-1509]; (2) the DNA phosphate groups may be considered stationary on the NMR time scale; (3) the relevant features of the spectra are determined solely by chemical shift anisotropy of the phosphorus atoms. The experimental and calculated spectra are in excellent agreement and support the validity of the above assumptions contrary to conclusions drawn in another investigation [Shindo, H., Wooton, J. B., Pheiffer, B. H., & Zimmerman, S. B. (1980) Biochemistry 19, 518-526]. In particular, we find no evidence to support the notion of a highly irregular phosphodiester backbone. Comparison of observed and simulated spectra allows the determination of the orientation of the 31P chemical shielding tensor relative to the bonding framework of the phosphodiester group. The orientation agrees with that expected from NMR studies of phosphodiester model compounds [Kohler, S. J., & Klein, M. P. (1976) Biochemistry 15, 967-973; Herzfeld, J., Griffin, R. G., & Haberkorn, R. A. (1978) Biochemistry 17, 2711-2718] and X-ray diffraction of oriented fibers [Arnott, S., & Hukins, D. W. L. (1972) Biochem. Biophys. Res. Commun. 47, 1504-1509].

Animals↗
PubMed1977

Thermal unfolding transition of ribonuclease A measured by 2'-CMP binding.

We report an approach to the problem of detecting and characterising intermediates in the unfolding of ribonuclease A. Two distinct properties of the protein are compared at equilibrium within the unfolding transition zone: (1) a physical property of the protein, the absorbance of buried tyrosine residues, and (2) a functional property, the ability to bind the specific ligand, 2'-CMP. A direct comparison of these two properties is made within the pH 5.8 transition zone, and an indirect comparison is made by using the stopped-flow instrument to sample rapidly the equilibrium properties of the pH 2.0 transition. At both pH 2.0 and pH 5.8, the results indicate that there are no intermediates in folding which have the physical properties of the native enzyme but which have lost the ability to bind a specific ligand.

Cytosine Nucleotides↗
PubMed1976

Guanidine-unfolded state of ribonuclease A contains both fast- and slow-refolding species.

The kinetics of the refolding reaction of ribonuclease A from high concentrations of guanidine hydrochloride or urea are biphasic, and show two refolding reactions whose rates differ 450-fold at pH 5.8 and 25 degrees. Measurements of cytidine 2'-phosphate binding during refolding, after stopped-flow dilution of guanidine hydrochloride (Gdn.HCl) or urea, show that functional bovine pancreatic ribonuclease A (RNase A; ribonucleate 3'-pyrimidino-oligonucleotidohydrolase, EC 3.1.4.22) is formed in both the fast and slow phases of the refolding process. We conclude that the guanidine-unfolded state of RNase A is an equilibrium mixture of fast- and slow-refolding species, as was found previously for the heat-unfolded state at low pH. The fraction of the fast-refolding species in guanidine or urea-unfolded RNase A is the same as that in the heat-unfolded protein at pH 2. Previous work has shown that the fast-refolding species disappears as the pH is raised from 3 to 5 for heat-unfolded RNase A. This pH effect is not present in refolding from concentrated Gdn.HCl solutions: the same proportion of the fast-refolding species is found from pH 2 to pH 6, and also from 2 M to 6 M Gdn.HCl at pH 5.8. We conclude that the same proportion of the fast-refolding species is present at equilibrium whenever the residual structure in unfolded RNase A is reduced to a low level, and that the structural difference between the fast-refolding and slow-refolding species of RNase A lies in the configuration of the random coil polypeptide chain.

Binding Sites↗