PubMed Health⌕ Search

Biomedical subjects

D A Torchia

Publications and source records attributed to D A Torchia.

89 records · Page 5Linked to original sources
PubMed1977

Investigation of molecular motion of proteoglycans in cartilage by 13C magnetic resonance.

13C nmr spectral parameters were measured for intact bovine nasal cartilage tissue, the purified proteoglycan aggregate, and chondroitin 4-sulfate. A comparison of integrated intensities obtained for four different samples of fresh tissue with an ethylene glycol standard indicated that at least 80% of the total glycosaminoglycan carbons in the tissue contributed to the spectrum. This result was confirmed by intensity measurements obtained at 56 degrees on fresh tissue and at 37 degrees after extensive papain digestion of fresh tissue. Spin lattice relaxation times and nuclear Overhauser enhancements were analyzed in terms of the following models of molecular motion: (a) single correlation time; (b) log X2 distribution of correlation times; and (c) anisotropic motion. The analysis indicates that the segmental motions of glycosaminoglycan chains are characterized by a broad distribution of correlation times centered at about 50 ns. Slow motion contributions to glycosaminoglycan line widths were reduced by dipolar decoupling (gammaH2/2pi = 65 kHz). Collagen intensity was observed in dipolar decoupled spectra, but not in scalar decoupled spectra of intact tissue, showing that the type II collagen in cartilage undergoes anisotropic motion like the type I collagen in tendon. Only glycosaminoglycan resonances were observed in spectra of a solution of proteoglycan aggregate before and after chondroitinase digestion. After subsequent digestion with papain, protein resonances were observed. These results suggest that the protein portions of the proteoglycan aggregate structure, in contrast with the glycosaminoglycan chains, have restricted backbone mobility and consequently a defined backbone structure.

Amino Acids↗
PubMed1977

A 13C magnetic resonance study of embryonic chick aorta.

13C nmr spectra of defatted aorta, obtained from chick embryos, ranging in age from 13 to 20 days, showed that linewidths were independent of the age of the embryo, this, in spite of the fact that crosslinking increases with age. As expected the dipolar decoupled spectrum of defatted aorta had a larger C-H signal intensity than the scalar decoupled spectrum, since collagen in the sample contributes signal intensity only in the former case. Significantly, the dipolar decoupled spectrum of autoclaved aorta also had a larger C-H signal intensity. This result indicates that ca. 30% of the carbons in the tissue, swollen by 0.15 M NaCl, has restricted motion at 37 degrees. Preliminary data indicate that tissue culture techniques can be used to enrich specific amino acids in chick aorta with 13C, thereby affording a means to study possible differences in molecular structure of the chemically distinct regions in elastin.

Animals↗
PubMed1976

Preparation of intact monomeric collagen from rat tail tendon and skin and the structure of the nonhelical ends in solution.

Procedures for the preparation of soluble collagen from rat skin and tail tendon were reviewed and revised to permit the preparation of native monomeric collagen with intact nonhelical ends. The degree of intactness was estimated from the tyrosine content, which is present only in the nonhelical ends, and by mobility of the COOH-terminal cyanogen bromide peptide of the alpha1 chain on sodium dodecyl sulfate gels. The amount of covalently cross-linked polymeric material present was estimated by molecular sieve chromatography of denatured samples. Rapid purification in the cold was sufficient to prevent or greatly reduce proteolytic alteration. Fractionation by salt precipitation at acid pH was effective in reducing the content of polymeric material. Rat tail tendon yielded completely intact native collagen, but some high molecular weight aggregates remained. Collagen from the skin of lathyritic rats was easier to obtain free of aggregates, but contained about 1 less tyrosine residue per alpha1 chain even when isolated in the presence of enzyme inhibitors. Proton NMR spectra of denatured acidic solutions of these preparations showed that 4 to 5 tyrosine residues per alpha chain were present, confirming the chemical analysis. Spectra of the native molecule showed that about the same number of tyrosine residues per chain are in rapid motion, unlike residues in the helical portion of the molecule, a result which shows that the nonhelical ends of the native molecule are unstructured in acidic solution.

Amino Acids↗
PubMed1975

Molecular mobility and structure of elastin deduced from the solvent and temperature dependence of 13C magnetic resonance relaxation data.

13C relaxation parameters, T1, line width, and NOE, have been determined for backbone carbons of ligamentum nuchae elastin swollen by 0.15 M NaCl, 0.15 M NaCl-formamide, 0.15 M NaCl-ethanol, dimethyl sulfoxide, and formamide. The data have been analyzed in terms of (a) a single correlation time model and (b) a model employing a log-chi2 distribution of correlation times used by Schaefer (1973) to analyze solid cis-polyisoprene 13C relaxation data. Employing the latter mode, one obtains an approximately self-consistent quantitative analysis of all the elastin data. An average backbone correlation time, tau, of ca. 2 nsec is calculated for elastin swollen in the presence of polar organic solvents at 37 degrees, in approximate agreement with tau of 0.4 nsec obtained for bulk cis-polyisoprene at 35 degrees. The influence of solvent and temperature on elastin spectra indicate that the larger tau value (approximately 80 nsec) obtained for elastin swollen by 0.15 M NaCl at 37 degrees is a consequence of weak interchain polar and hydrophobic interactions, a result which is in accord with the reported viscoelastic behavior exhibited by water-swollen elastin at 37 degrees. The results obtained further suggest that Gly, Pro, and Val residues are significantly more mobile than Ala residues, which are located in the cross-link regions. Hence, the NMR data support the view that water-swollen elastin is composed of a network of mobile chains, except possibly in the cross-link regions.

Animals↗
PubMed1975

Molecular dynamics and structure of the random coil and helical states of the collagen peptide, alpha 1-CB2, as determined by 13C magnetic resonance.

Carbon-13 chemical shifts, spin-lattice (T1) and spin-spin (T2) relaxation times, and 13C-[1H] nuclear Overhauser enhancements (NOE) have been determined for the random coil and triple helical states of the alpha 1-CB2 fragment of rat skin collagen. Assignment of all aliphatic resonances of this 36 residue peptide in the random coil state (30 degrees) has been achieved with the aid of model polypeptides containing pyrrolidine residues. The chemical shifts and intensities of the Pro and Hyp C-gamma resonances show that (see article) 90% of the X-Pro and X-Hyp bonds are trans in both helix and coil conformations. From T1 measurements rotational correlation times (tau-eff) of ca. 0.45 nsec are calculated for interior C-alpha carbons in the coil, while taueff values of the side chain and near terminal carbons are found to be 2-9 times smaller. These results along with the narrow natural line widths (3-5 Hz) and maximal NOE values (2.8 plus or minus 0.3) demonstrate the high degree of backbone mobility, due to segmental motion, in the unordered state of the peptide. By contrast, the broad lines (50-90 Hz) and small NOE values (1.3 plus or minus 0.3) for the alpha carbons in the helical state (2 degrees) suggest much slower motion. The line widths and NOE values together with the C-alpha T1 values (0.025-0.040 sec) correspond to correlation times which are in reasonable agreement with those calculated for an axially symmetric rigid ellipsoid, undergoing rotational diffusion, having dimensions approximating those of a collagen-type triple helical aggregate of three alpha 1-CB2 chains. A satisfactory computer simulation of the experimental 2 degrees spectrum is obtained by assigning the narrow aliphatic resonances in the spectrum (line widths 5-40 Hz) to (a) carbons in the small amounts of alpha 1-CB2 (3 mol %) and alpha 1-CB1 (2.5 mol %) random coil conformations, (b) carbons in the flexible terminal triplets of the helix, and (c) Ala, Leu, and Phe methyl and phenyl carbons. The side chain carbon line widths obtained from the simulation--when compared with side chain line widths calculated for a rotating rigid ellipsoid with internal motion--indicate rapid axial reorientation of methyl and phenyl groups. With the exception of the Hyp residue the line widths suggest local motion for at least some carbons in most other side chain moieties. The Hyp C-beta and C-gamma line widths indicate the presence of little if any rapid Hyp ring motion.

Animals↗
PubMed1972

Conformational interconversions of the cyclic hexapeptide cyclo(Pro-Gly) 3 .

A cyclic hexapeptide, cyclo(Pro-Gly-Pro-Gly-Pro-Gly), has been synthesized; its solution conformations were examined by 220-MHz nuclear magnetic resonance spectroscopy. The solution structures have been deduced, and shown to vary as a function of solvent polarity. In addition, it has been found that this cyclic peptide binds alkali metal cations. While the predominant conformation of this cyclic peptide is 3-fold symmetric in the apolar solvent methylene chloride, an asymmetric structure is preferred in some polar solvents (water, dimethylsulfoxide). However, addition of alkali metal salts, such as sodium thiocyanate, to dimethylsulfoxide solutions of the peptide shifts the conformational equilibrium in favor of a second type of C(3)-symmetric structure, presumably the result of the formation of a stable peptide-metal ion complex. Nuclear magnetic resonance data suggest that the peptide in methylene chloride solution takes up a conformation containing three cis' Pro C(alpha)-C=O bonds and three cis Gly-Pro peptide bonds; that water and dimethylsulfoxide stabilize a conformer in which one (or two) sets of such bonds of a given Pro-Gly unit have undergone interconversion to trans'/trans forms; and that alkali metal cations complex the cyclic peptide in a C(3)-symmetric all-trans'/trans structure.

Butanols↗