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T Atkinson

Publications and source records attributed to T Atkinson.

176 records · Page 10Linked to original sources
PubMed1979

Isolation and partial characterization of four plasmids from antibiotic-resistant thermophilic bacilli.

Twenty-nine antibiotic-resistant isolates of thermophilic bacilli were examined for the presence of covalently closed circular duplex DNA molecules by agarose-gel electrophoresis and caesium chloride-ethidium bromide density gradient centrifugation. Five of the 29 strains tested contained covalently closed circular molecules. Two of the streptomycin-resistant strains contained the same two plasmids: pAB118A of molecular weight 4.9 X 10(6) (7.0 kilobases) and pAB118B of molecular weight 3.0 X 10(6) (4.3 kilobases). Two of the tetracycline-resistant strains each contained a plasmid (pAB124) of molecular weight 2.9 X 10(6) (4.14 kilobases), while a third harboured a small plasmid (pAB128) of molecular weight 2.5 X 10(6) (3.57 kilobases). These plasmids were digested with 19 different restriction endonucleases and the numbers of cleavage sites were determined. Transformation of Bacillus subtilis (168 (Trp-) with purified plasmid DNA indicated that pAB124 conferred tetracycline resistance on the host.

Anti-Bacterial Agents↗
PubMed1978

A specific endonuclease from Bacillus caldolyticus.

The purification and characterization of a new restriction endonuclease, BclI from the extreme thermophile Bacillus caldolyticus is reported. This enzyme recognizes the sequence : formula: (see text) and cleaves at the positions indicated by the arrows.

Bacillus↗
PubMed1977

Enhanced plasma persistence of therapeutic enzymes by coupling to soluble dextran.

Conjugation of carboxypeptidase G and arginase, two enzymes of therapeutic interest, to a soluble dextran significantly enhanced plasma persistence in normal and tumour-bearing mice. A prolonged decrease in arginine concentrations in plasma of tumour-bearing mice was demonstrated by using the dextran-linked arginase. Gel filtration of dextran-enzyme conjugate showed that enzyme activity co-chromatographed as a single peak with carbohydrate, and enzyme was shown to be covalently linked to the dextran.

Animals↗
PubMed1975

Gram-scale purification of methionyl-tRNA and tyrosyl-tRNA synthetases from Escherichia coli.

A procedure is presented for the purification of 3 g of homogeneous methionyl-tRNA synthetase and 1 g of homogeneous tyrosyl-tRNA synthetase from 50 kg batches of Escherichia coli. The procedure permits the isolation of many enzymes simultaneously and the elution positions of seven other aminoacyl-tRNA synthetases, catalase, rhodanese, phosphofructokinase, elongation factor Tu and cytochrome b-562 are indicated. The problems of extraction work on this scale are discussed.

Amino Acyl-tRNA Synthetases↗
PubMedDate not supplied

Protein kinase activities in cell-free extracts of Streptomyces coelicolor A3(2).

Protein kinase activities were detected in cell-free extracts of the B385 derivative of Streptomyces coelicolor A3(2); at least 12 polypeptides, ranging in Mr from 6,000 to 98,000, were detectably phosphorylated, probably as O-monoesters, after incubation with gamma [32P]ATP. The culture stage of the mycelia used for production of the cell-free extracts determined the profile of phosphorylated polypeptides. Phosphoenol pyruvate acted as a potent modulator of the apparent degree of protein kinase activity. In addition Ca2+ ions, verapamil, chlorpromazine and anti-calmodulin antiserum had specific effects on the profile of phosphopolypeptides observed.

Autoradiography↗
PubMedDate not supplied

Site-directed mutagenesis reveals role of mobile arginine residue in lactate dehydrogenase catalysis.

The binding of substrates to lactate dehydrogenases induces a marked rearrangement of the protein structure in which a 'loop' of polypeptide (residues 98-110) closes over the active site of the enzyme. In this rearrangement, arginine 109 (a basic residue conserved in all known lactate dehydrogenase sequences and in the homologous malate dehydrogenases) moves 0.8 nm from a position in the solvent to one in the active site where its guanidinium group resides within hydrogen bonding distance of both the reactive carbonyl of pyruvate and imidazole ring of the catalytic histidine 195 (see Fig. 1). Whilst this feature of the enzyme has been commented upon previously, the function of this mobile arginine residue during catalysis has not been tested experimentally. The advent of protein engineering has now enabled us to define the role of this basic residue by substituting it with the neutral glutamine. Transient kinetic and equilibrium studies of the mutant enzyme indicate that arginine 109 enhances the polarization of the pyruvate carbonyl group in the ground state and stabilizes the transition state. The gross active-site structure of the enzyme is not altered by the mutation since an alternative catalytic function of the enzyme (rate of addition of sulphite to NAD+), which does not require hydride transfer, is insensitive to the arginine----glutamine substitution.

Arginine↗
PubMedDate not supplied

Kinetic studies of plasminogen activation by epithelial tissue plasminogen activator.

Initial-rate kinetic studies of the activation of plasminogen by epithelial activator were performed in the absence and in the presence of fibrinogen and CNBr-digested fibrinogen, under assay conditions similar to those described by Hoylaerts et al. (J Biol Chem, 257, 2912, 1982). In the purified system, and in the absence of any stimulator, Lys-plasminogen is more readily activated than Glu-plasminogen, with catalytic rate constants of 0.01 s-1 and 0.0034 s-1 and Michaelis constants of 1.2 microM respectively. With Glu-plasminogen, double reciprocal plots deviated from linearity at low concentrations of plasminogen, in agreement with the findings reported for melanoma activator. In the presence of fibrinogen, activation rates for both Lys and Glu-plasminogen were increased. (kcat = 0.017 and 0.041 s-1 and km = 1.4 and 41 microM, respectively). In the presence of CNBr-fragments of fibrinogen, the Michaelis constant is lowered for both forms of plasminogen, (km = 0.3 microM) thus indicating high affinity and efficient activation of plasminogen on fibrin clot. Comparison of the kinetic data with those reported for melanoma activator suggest that even though the values of the kinetic constants are different, epithelial activator has a similar mechanism of action for the activation of plasminogen as the melanoma enzyme.

Cyanogen Bromide↗