Biomedical subjects

Peter A Williams

Publications and source records attributed to Peter A Williams.

22 records · Page 2Linked to original sources

PubMed1997

XylUW, two genes at the start of the upper pathway operon of TOL plasmid pWW0, appear to play no essential part in determining its catabolic phenotype.

The upper pathway operon of the toluene catabolic pathway of TOL plasmid pWW0 was shown to carry two open reading frames between the start of transcription and xylC (encoding benzaldehyde dehydrogenase), the first previously reported gene of the operon. These were designated xylUW: xylU encoded a protein of 131 amino acid residues (M(r) 14,244) which bore no relationship with any protein in the databases, and xylW encoded a protein of 348 residues (M(r) 36,992) which was strongly homologous to other long-chain Zn-containing alcohol dehydrogenases. Extracts of Escherichia coli carrying xylUW in expression vector pTrc99A contained a novel protein corresponding to XylW, but no NAD(+)-dependent dehydrogenase activity against benzyl alcohol, mandelate or bezylamine. A mini-Tn5 transposon carrying the meta pathway operon was constructed and from it two strains of Pseudomonas putida were constructed with the normally plasmid-encoded catabolic operons integrated into the chromosome. Three derivatives of plasmid pKNG101 containing modified xylUW genes were constructed, two of which had frameshifts in xylU and xylW, respectively, and a third with a deletion from the 3' end of xylU into the 5' end of xylW. The wild-type genes of the two Pseudomonas strains were substituted by the mutant alleles by reverse genetics. The ability of the constructed mutant strains to utilize the aromatic substrates of the TOL pathway was not significantly affected.

Amino Acid Sequence↗

PubMedDate not supplied

Asymmetrical-flow field-flow fractionation with on-line multiangle light scattering detection. 1. Application to wormlike chain analysis of weakly stiff polymer chains.

Four samples of hyaluronan in the sodium form, ranging in weight-average molecular weight, M(w), from 6.67 x 10(5) to 4.23 x 10(6) were investigated by asymmetrical-flow field-flow fractionation coupled to multiangle light scattering (FlFFF-MALS) in 0.2 M aqueous NaCl at 25 degrees C. M(w) and z-average radii of gyration, R(G)(z)(), obtained via FlFFF-MALS showed a good agreement with the results obtained by conventional static light scattering. Furthermore, the molecular weight dependence of the radius of gyration for sodium hyaluronan obtained via FlFFF-MALS was analyzed on the basis of the Kratky-Porod model for unperturbed wormlike chains combined with the Yamakawa theory for radius expansion factor, and a sufficiently good agreement was observed between the theoretical prediction and experimental data. These results show the potential usage of FlFFF-MALS regarding size separation and molecular characterization even for weakly stiff chains.

Fractionation, Field Flow↗

PubMedDate not supplied

Physicochemical characterization of konjac glucomannan.

Four commercial konjac glucomannan (KGM) samples and a glucomannan derived from yeast were characterized by aqueous gel permeation chromatography coupled with multi angle laser light scattering (GPC-MALLS). Disaggregation of aqueous glucomannan solutions through controlled use of a microwave bomb facilitated reproducible molar mass distribution determination alleviating the need for derivatization of the polymer or the use of aggressive solvents. Further characterization was undertaken by use of capillary viscometry and photon correlation spectroscopy (PCS). The weight average molecular masses (M(w)) determined were in the region of 9.0 +/- 1.0 x 10(5) g mol(-1) for KGM samples and 1.3 +/- 0.4 x 10(5) g mol(-1) for the yeast glucomannan. The values determined for KGM in aqueous solution are in agreement with those reported for KGM in aqueous cadoxen. The degradation of samples observed upon autoclaving has been quantified by GPC-MALLS and intrinsic viscosity determination, allowing comparison with reported Mark-Houwink parameters. Shear flow experiments were undertaken for a range of KGM solutions of concentration 0.05 to 2.0% using a combination of controlled stress and controlled strain rheometers. The concentration dependence of the zero shear specific viscosity was determined by analysis of the data using the Ellis model. The dependence of the zero shear specific viscosity on the coil overlap parameter was defined and interpretation discussed in terms of the Martin and Tuinier equations.

Chromatography, Gel↗

PubMedDate not supplied

New insights into the mechanism of gelation of alginate and pectin: charge annihilation and reversal mechanism.

Studies have been undertaken on the binding of Mn2+ ions to two alginate samples of different mannuronate:guluronate ratios (M:G), a sample of low-ester amidated pectin and poly(acrylic acid) (PAA). The binding of Ca2+ ions has also been included for the latter for comparison. The binding curves showed an initial steep rise at low additions of Mn2+ or Ca2+ indicating that all of the ions were bound to the polymer chains with none remaining in solution. At higher additions, the binding curves showed a plateau region and the maximum amount bound, theta, was found to be 0.2, 0.2, 0.25, and 0.33 mol M(2+)/mol COO- for high M:G alginate, low M:G alginate, pectin, and PAA, respectively. The binding curves for Mn2+ and Ca2+ with PAA were superimposable. In all cases, theta was less than the stoichiometric equivalent and also less than predicted by Manning counterion condensation theory. The linear charge density, xi, for the polymers is 1.49, 1.55, 1.62, and 2.85, and it was found that at maximum binding the effective linear charge density, xi(effective), decreased to a value close to 1 in each case and not 0.5 as predicted from Manning's two-variable theory. The mobility of the PAA chains has been followed by electron spin resonance spectroscopy using nitroxide spin labels covalently attached to the polymer, and the gelation of the pectin and alginate samples has been monitored using small deformation oscillatory experiments. For PAA at maximum binding, it was noted that there was a loss of chain mobility and precipitation. For pectin and alginate, gelation occurred and the stoichiometric ratio for maximum binding corresponded to the stoichiometric ratio for the maximum in G'. Precipitation and gelation are attributed to the formation of polymer-metal complexes involving one or two carboxylate groups resulting in charge reversal or charge annihilation.

Alginates↗