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J R Knox

Publications and source records attributed to J R Knox.

At least 55 records · Page 3Linked to original sources
PubMed1987

Crystallization and preliminary X-ray and optical spectroscopic characterization of the photochemical reaction center from Rhodobacter sphaeroides strain 2.4.1.

The photochemical reaction center from Rhodobacter sphaeroides 2.4.1 has been crystallized. The crystals were obtained in a solution of beta-octylglucoside by the vapor diffusion technique using polyethylene glycol 4000 as the precipitant at 22 degrees C. The orthorhombic crystals (space group P2(1)2(1)2(1)) have cell constants a = 142.5 A, b = 136.1 A, c = 78.5 A, and diffract to 3.7 A. The crystals display pronounced linear dichroism in the carotenoid absorption spectral region.

Bacterial Proteins↗
PubMed1986

The association behaviour of beta-lactamases. Sedimentation equilibrium studies in ammonium sulphate solutions.

The beta-lactamases (EC 3.5.2.6) from TEM plasmid RP4, Bacillus licheniformis 749/C and Enterobacter cloacae P99 were studied in solution over a wide concentration range by equilibrium sedimentation. Though crystal symmetries indicate that all three enzymes are potentially dimeric in their crystal forms, in 50 mM-sodium cacodylate at pH 6.5 the enzymes show only a small tendency to associate, indicated by a weight-average Mr (Mw) at 3% (w/v) concentration about 9% greater than that of the monomer. Although the mode of association could not be determined, this extent of association corresponded to a dimerization constant of about 2 X 10(2) M-1. In 2.1 M-(NH4)2SO4 the B. licheniformis enzyme shows some association at concentrations over 1%, displaying an Mw value at 7% concentration about 60% more than the monomer. Under the same conditions Mw for the Entero. P99 enzyme is about 60% greater than the monomer near the solubility limit of about 2%. However, the Mw for the TEM enzyme is over twice that of the monomer at its solubility limit (3%) in 1.7 M-(NH4)2SO4. Fitting the sedimentation data of the TEM enzyme in 1.7 M-(NH4)2SO4 with a dimerization model and an indefinite-isodesmic-association model yielded equilibrium constants of 1.5 X 10(4) and 3.3 X 10(2) M-1 respectively, with the indefinite-isodesmic model giving the better fit. Fitting the data for the other two enzymes yielded values of 1.4 X 10(3) and 1.7 X 10(2) M-1 respectively for the Entero. P99 enzyme and 4.5 X 10(2) and 45 M-1 respectively for the B. licheniformis enzyme. It could not be determined which model was the better fit for these two enzymes. Since none of the beta-lactamases studied here showed strong evidence of the terminal aggregate being a dimer, we conclude that crystalline dimers, if they exist, will not be tightly associated or physiologically significant.

Ammonium Sulfate↗
PubMed1986

On the origin of bacterial resistance to penicillin: comparison of a beta-lactamase and a penicillin target.

Structural data are now available for comparing a penicillin target enzyme, the D-alanyl-D-alanine-peptidase from Streptomyces R61, with a penicillin-hydrolyzing enzyme, the beta-lactamase from Bacillus licheniformis 749/C. Although the two enzymes have distinct catalytic properties and lack relatedness in their overall amino acid sequences except near the active-site serine, the significant similarity found by x-ray crystallography in the spatial arrangement of the elements of secondary structure provides strong support for earlier hypotheses that beta-lactamases arose from penicillin-sensitive D-alanyl-D-alanine-peptidases involved in bacterial wall peptidoglycan metabolism.

Amino Acid Sequence↗
PubMed1985

2.8-A Structure of penicillin-sensitive D-alanyl carboxypeptidase-transpeptidase from Streptomyces R61 and complexes with beta-lactams.

The crystallographic structure of the penicillin-sensitive D-alanyl carboxypeptidase-transpeptidase from Streptomyces R61 has been solved to 2.8-A resolution. The 38,000-dalton serine peptidase has two regions of secondary structure, an alpha/beta cluster, and a region which contains five helical segments. The beta sheet is composed of five beta strands. The tertiary structure has no homology with the classic serine proteases or with the zinc carboxypeptidases. The binding at a common site of three types of beta-lactam (a penicillin, a cephalosporin, a monocyclic beta-lactam) and a desazacyclobutanone has been observed in Fourier difference maps. The binding site sequence is Val-Gly-Ser-Val-Thr-Lys. The beta-lactam ring lies near the enzyme's catalytic serine at position 37, and the C3 substituent of a cephalosporin falls near lysine 40.

Anti-Bacterial Agents↗
PubMed1985

Crystallization and preliminary X-ray data for the exocellular beta-lactamase of Bacillus licheniformis 749/C.

The exocellular beta-lactamase from Bacillus licheniformis 749/C has been crystallized from polyethylene glycol solution at pH 5.5. An X-ray examination of the monoclinic crystals shows the space group is P21, with unit cell dimensions a = 66.77 A, b = 93.77 A, c = 43.57 A and beta = 104.5 degrees. The asymmetric unit consists of two molecules of 28,500 Mr each. The crystals are suitable for structure analysis to at least 2 A resolution.

Bacillus↗
PubMed1983

Crystallographic data for the beta-lactamase from Enterobacter cloacae P99.

The beta-lactamase from Enterobacter cloacae P99 has been crystallized from polyethylene glycol solution at pH 7. X-ray examination of the orthorhombic crystals shows the space group is P2(1)2(1)2 with unit cell dimensions a = 77.4 A, b = 69.4 A, and c = 63.6 A. There is one molecule of molecular weight 39,000 in the asymmetric unit.

Enterobacter↗
PubMed1982

Penicillin target enzyme and the antibiotic binding site.

The three-dimensional structure of a penicillin-sensitive D-alanyl-carboxypeptidase-transpeptidase has been determined by x-ray crystallography to a resolution of 2.8 angstroms. The site of binding of the beta-lactam antibiotics penicillin and cephalosporin has been located. These findings constitute direct observation of the interaction of beta-lactams with a transpeptidase enzyme and establish the feasibility of defining the molecular stereochemistry of this interaction for purposes of drug design.

Binding Sites↗
PubMed1981

Secondary structure relations between beta-lactamases and penicillin-sensitive D-alanine-carboxypeptidases.

The sequence homology found by Waxman & Strominger between penicillin-sensitive D-alanine-carboxypeptidases and penicillin-inactivating beta-lactamases is shown to extend to the level of secondary structure as predicted by the method of Chou & Fasman or by the informational method of Garnier et al. Thermodynamic similarity of homologous segments of these proteins is demonstrated by means of a sequence-independent parameter, the hydration potential of Wolfenden at al. Although the 40- to 70-residue amino-terminal sequences examined contain a common serine reactive with penicillins and (in the case of the carboxypeptidases) an R-D-alanyl-D-alanine substrate analog, no homology in secondary structure or hydration potential could be found with a serine protease such as alpha-chymotrypsin.

Amino Acid Sequence↗
PubMed1979

Predicted secondary structures of four penicillin beta-lactamases and a comparison with two lysozymes.

We have predicted the secondary structures of four beta-lactamases (Bacillus cereus, Bacillus licheniformis, Staphylococcus aureus, and Escherichia coli R-TEM) by the statistical method of Chou & Fasman as well as by the information theory method of Garnier et al. The secondary structures of all four beta-lactamases are of the alpha/beta type (Levitt & Chothia's nomenclature), with helices at N- and C-termini. There are about eight short regions each of alpha-helical (30--50%) and beta-strand (10--20%) structure separated by about 20 reverse turns. The conformation of the Gram-positive and Gram-negative beta-lactamases are generally similar although a few differences are predicted between the S.aureus and E.coli structures. Surprisingly, the two bacilli structures differ significantly in three short regions. In all four enzymes the region near the catalytically-implicated tyrosine has similar secondary structure. The secondary structure of hen egg white lysozyme, a penicillin-binding enzyme, as well as T4 phage lysozyme, has similarities to the N-terminal half of the penicillin-destroying beta-lactamases.

Amino Acid Sequence↗
PubMed1974

Toxaphene insecticide: a complex biodegradable mixture.

Adsorption and gas-liquid chromatography separate toxaphene into at least 175 polychlorinated 10-carbon compounds including Cl(6), Cl(7), Cl(8), Cl(9), and Cl(10) derivatives. One toxic component is 2,2,5-endo,6-exo,8,9,10-heptachlorobornane. Rats metabolically dechlorinate toxaphene, removing about half of the chlorine from the technical insecticide and from each of seven subfractions of varying composition and toxicity.

Animals↗