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Biomedical subjects

C R Jones

Publications and source records attributed to C R Jones.

At least 145 records · Page 8Linked to original sources
PubMed1978

Culture pH, CO2 tension, and cell division in Euglena gracilis Z.

Growth characteristics of Euglena gracilis Z as functions of culture pH, CO2 tension, temperature, and lighting regime were investigated. The results are consistent with the possibility that cell division is preceded by a lowered intracellular pH. Also consistent with this possibility is the finding that division rhythmicity can be induced by periodic changes in CO2 tension. It is suggested that the rhythmicity is induced by changes in intracellular pH produced by carbonic acid.

Carbon Dioxide↗
PubMed1978

The quantitation of nuclear Overhauser effect methods for total conformational analysis of peptides in solution. Application to gramicidin S.

The [1H:1H] nuclear Overhauser effects (NOE's) and spin-lattice relaxation times (T1's) are reported for the backbone protons of the decapeptide gramicidin S. Several methods for calculating interproton distances from these measurements are presented. Ratios of interproton distances were obtained from [1H:1H] NOE's and from the combination of [1H:1H]NOE'S and T1 values. Actual proton-proton distances were calculated from these ratios either by using the known distance between two geminal protons or distances derived from scalar coupling constants. The interproton distances calculated for gramicidin S are consistent with a II' beta-turn/antiparallel beta-sheet conformation.

Gramicidin↗
PubMed1977

Proton magnetic resonance study of conformational dynamics, coordianted internal motions, and chemical shifts of tocinamide.

All proton magnetic resonance lines of the NH-CHalpha-CH2beta fragments of five amino acid residues of the heterodetic peptide, tocinamide, have been analyzed, including reassigment of certain NH, CHalpha, and CH2beta resonances. The 1H NMR spectral parameters evaluated from this analysis include (a) all chemical shifts, (b) (3JNHCH), (3Jalpha beta), and (2Jbeta beta) values, and (c) temperature dependencies of these coupling constants and chemical shifts--the latter includes aliphatic and aromatic CH protons. The (3Jalpha beta) coupling constants yielded Calpha-Cbeta rotamer populations, Pi, for five residues and these were used to explore conformational dynamics and coordinated internal motions of tocinamide. The rotamer populations and their temperature dependencies established, (1) that all Calpha-Cbeta bonds exhibit extensive internal rotation; (2) that rotamer preferences exist for every residue; (3) that the 162 conformations possible for completely free rotation around every bond of the Calpha1-Cbeta1-S1-S6-Cbeta6-Calpha6 disulfide fragment can be reduced to two or three if the concept of coordinated internal motion is introduced. We reject the possibility of a frozen conformation for the Cys1-Cys6 fragment in the eclipsed, staggered, or nonclassical rotamer states and propose the following possibilities: (a) three classical rotamers populated in the ratio 60:25:15, (b) three nonclassical rotamers not differing by +/- 15 degrees from the classical values of 180 degrees, + 60 degrees, and -60 degrees, or (c) two nonclassical but noneclipsed rotamers with a third rotamer essentially zero, and (4) that the Calpha-Cbeta rotamer populations of the Tyr2-Cys1-S-S-Cys6 fragment are consistent with coordinated internal motions of the Calpha-Cbeta bonds of all three residues. The existence of temperature coefficients, deltadelta/deltaT, POF +/- 2 ppb/degrees C for aliphatic protons can be accounted for, in part, by postulating intrinsic rotamer chemical shifts which are temperature independent. Deltadelta/deltaT values should therefore be useful for investigating conformational dynamics. A further consequence of this interpretation is that greater care should be exercised in using deltadelta/deltaT values to assign hydrogen-bonded amide protons, especially when deltadelta/deltaT approximately -2 to -4 ppb/degrees C.

Amino Acids↗
PubMed1976

Quantitative determination of the number of secondary and tertiary structure base pairs in transfer RNA in solution.

Resonances in the low-field (11-15 ppm) nuclear magnetic resonance spectrum (NMR) of tRNA molecules arise from secondary and tertiary structure base pairs (1 resonance for each base pair) as well as tertiary structure hydrogen bonds. An accurate method for integrating the low-field spectra has been developed and applied to seven different tRNA. In the presence of high levels of magnesium (10 mM free magnesium) the number of resonances (base pairs) per molecule is typically 3-4 more than the number predicted by the cloverleaf model. These results confirm our recent proposal that, under proper conditions, most tRNA exhibit 3-4 tertiary structure interactions in solution, which are also observed in x-ray diffraction studies of yeast tRNAPhe. In addition to common resonances in the 11-15 ppm region, there are common resonances at 10.5 and 9.5 ppm. A critique of methods used to integrate the low-field spectra is given and possible sources of error are indicated. The discrepancy between our present results and previous studies, which indicated that the number of base pairs per molecule was close to the number predicted by the cloverleaf model, can be attributed partly to differences in magnesium concentration and partly to inaccuracies inherent in the integration methods used.

Escherichia coli↗
PubMed1975

Identification of a unique ethidium bromide binding site on yeast tRNAPhe by high resolution (300 MHz) nuclear magnetic resonance.

The binding of ethidium bromide to yeast tRNAPhe has been studied by high resolution (300 MHz) proton nuclear magnetic resonance. Under appropriate experimental conditions one ethidium bromide is bound to each tRNA and two resonances from ring NH protons are shifted upfield. These observations taken in conjunction with the low-field spectrum of yeast tRNAPhe show that the unique ethidium bromide binding site is located between base pairs AU6 and AU7 of the amino acid acceptor stem. This information should be of value in understanding the way in which ethidium bromide binding alters the biochemical properties of the tRNA molecules.

Binding Sites↗
PubMed1975

Close-up photography in the dental office.

Photographs taken by the dentist can be used in his professional contacts, in office administration, and for patient education and motivation. The parts of a camera including viewing systems, lenses, shutters, diaphragm, and film are described. The technique for close-up, intraoral photography requires special lens systems and proper lighting. The correct method for focusing is described.

Dental Assistants↗
PubMed1974

Investigation of the structure of yeast tRNAphe by nuclear magnetic resonance: paramagnetic rare earth ion probes of structure.

The binding of paramagnetic rare earth ions to yeast tRNA(Phe) shifts some resonances in the low-field nuclear magnetic resonance spectrum that have been assigned to ring nitrogen protons of specific Watson-Crick base pairs. The changes in the nuclear magnetic resonance spectrum as the tRNA is titrated with Eu(3+) indicate that 4 (or 5) Eu(3+) ions are tightly bound, that the metal binding is in the fast exchange limit, and that the binding to different sites in the molecule is sequential rather than cooperative. The first metal bound simultaneously shifts resonances associated with the dihydrouridine and the -C-C-A stem. This permits us to conclude that the folding of the tRNA(Phe) in solution brings the phosphate backbone of the -C-C-A and the dihydrouridine stems into close proximity. A model of the three-dimensional structure of tRNA(Phe) incorporating this new information appears to be compatible with the results obtained from x-ray diffraction.

Europium↗