Biomedical subjects

D J Shaw

Publications and source records attributed to D J Shaw.

At least 127 records · Page 7Linked to original sources

PubMed1982

Characterization of Escherichia coli men mutants defective in conversion of o-succinylbenzoate to 1,4-dihydroxy-2-naphthoate.

Four independent menaquinone (vitamin K2-deficient mutants of Escherichia coli, blocked in the conversion of o-succinylbenzoate (OSB) to 1,4-dihydroxy-2-naphthoate (DHNA), were found to represent two distinct classes. Enzymatic complementation was observed when a cell-free extract of one mutant was mixed with extracts of any of the remaining three mutants. The missing enzymes in the two classes were identified by in vitro complementation with preparations of OSB-coenzyme A (CoA) synthetase or DHNA synthase isolated from Mycobacterium phlei. Mutants lacking DHNA synthase (and therefore complementing with M. phlei DHNA synthase) were designated menB, and the mutant lacking OSB-CoA synthetase (and therefore complementing with M. phlei OSB-CoA synthetase) was designated menE. The menB mutants produced only the spirodilactone form of OSB when extracts were incubated with [2,3-14C2]OSB, ATP, and CoA; the OSB was unchanged on incubation with an extract from the menE mutant under these conditions. Experiments with strains lysogenized by a λ men transducing phage (λG68) and transduction studies with phage P1 indicated that the menB and menE genes form part of a cluster of four genes, controlling the early steps in menaquinone biosynthesis, located at 48.5 min in the E. coli linkage map. Evidence was obtained for the clockwise gene order gyrA....menC-E⃰ -B-D, where the asterisk denotes the uncertain position of menE relative to menC and menB. The transducing phage (λG68) contained functional menB, menC, and menE genes, but only part of the menD gene, and it was designated λ menCE⃰ B(D).

Chromosome Mapping↗

PubMed1981

Molecular cloning of the fnr gene of Escherichia coli K12.

Mutations in the fnr gene of Escherichia coli have pleiotrophic effects leading to deficiencies in the reduction of fumarate and nitrate, hydrogen production and the ability to grow anaerobically with fumarate or nitrate as terminal electron acceptors. Transducing phages (lambda fnr) carrying the wild-type fnr gene were isolated from populations of artificially-constructed recombinant lambda phages by their ability to complement the lesions of fnr mutants. The lambda fnr phages restored anaerobic growth with fumarate and nitrate as electron acceptors and as prophages, they promoted normal synthesis of fumarate reductase, nitrate reductase and hydrogenase in fnr mutants. Five independently-isolated lambda fnr phages each contained a R.HindIII fragment (11.5 kilobases) that possessed three internal R.EcoRI targets and had inserted with the same orientation relative to the phage. A physical map of the fnr region was constructed by restriction analysis and flanking fragments were identified by DNA : DNA hybridization.

Anaerobiosis↗

PubMed1981

Molecular cloning of menaquinone biosynthetic genes of Escherichia coli K12.

A transducing phage carrying some of the genes (men) defining the early stages of menaquinone biosynthesis was isolated from a pool of recombinant lambda phages that had been constructed from R.HindIII digests of E. coli DNA and the corresponding insertion vector. The lesions of menB and menC mutants were complemented by the phage but menD mutants were transduced either at low frequencies or not at all. This indicates that the transducing phage contains functional menB and menC genes but that only part of the menD gene had been cloned. The phage (lambda G68) was accordingly designated lambda menCB(D). Studies with the transducing phage enabled earlier mapping data (Guest 1979) to be reinterpreted in favour of the gene order nalA....menC..menB..MenD....purF. Restriction analyses established the presence of a bacterial DNA fragment (11.5 kb) linked by a R.HindIII target to the right arm of the lambda genome but fused to the left arm of the vector. Hybridization studies confirmed that the cloned DNA was derived from a larger R.HindIII fragment (21 kb). A physical map of the men region was constructed and some flanking and overlapping fragments were identified.

Bacteriophage lambda↗

PubMed1980

Substrate specificity and other properties of the inducible S3 secondary alkylsulphohydrolase purified from the detergent-degrading bacterium Pseudomonas C12B.

The inducible S3 secondary alkylsulphohydrolase of the soil bacterium Pseudomonas C12B was purified to homogeneity (683-fold from cell-free extracts by a combination of column chromatography on DEAE-cellulose. Sephadex G-100 and Blue Sepharose CL-6B. The enzyme has a molecular weight in the region of 40000--46000, and is active over a broad range of pH from 5 to 9, with maximum activity at pH 8.2. The preferred substrates of the enzyme are the symmetrical secondary alkylsulphate esters such as heptan-4-yl sulphate and nonan-5-yl sulphate and the asymmetric secondary octyl and nonyl sulphate esters with the sulphate group attached to C-3 or C-4. However, for each asymmetric ester, the L-isomer is much more readily hydrolysed than the D-isomer. This specificity is interpreted in terms of a three-point attachment of the substrate to the enzyme's active site. The alkyl chains on either side of the esterified carbon atom are bound in two separate sites, one of which can only accommodate alkyl chains of limited size. The third site binds the sulphate group. Enzymic hydrolysis of this group is accompanied by complete inversion of configuration at the asymmetric carbon atom. The implied cleavage of the C--O bond of the C--O--S ester linkage was confirmed by 18O-incorporation studies.

Binding Sites↗

PubMed1980

An improved procedure for the preparation of alkyl sulphate esters suitable for the study of secondary alkylsulphohydrolase enzymes.

A simple, rapid and convenient method for the synthesis of secondary alkyl sulphate esters is described in which the sodium alkoxide of the parent alcohol is sulphated by using triethylamine-SO3 complex. The procedure gives relatively good yields, even for the sulphation of long-chain alcohols and those in which the hydroxy group is remote from the terminal carbon atoms. Positional isomerization, arising from the migration of the hydroxy group along the carbon chain, is absent, and resolved enantiomers of alcohols react with complete retention of configuration.

Alcohols↗

PubMed1977

The mechanism of action of primary alkylsulphohydrolase and arylsulphohydrolase from a detergent-degrading micro-organism.

Previous studies have shown that secondary alkylsulphohydrolases from certain detergent-degrading micro-organisms are unusual esterases in that they catalyse fission of the C-O bond of the alkyl sulphate ester linkage. The position of bond fission catalysed by a primary alkylsulphatase and an arylsulphohydrolase present in Pseudomonas C12B has now been investigated. The primary alkylsulphatase behaved like the secondary alkylsulphohydrolases in cleaving the C-O bond of potassium heptan-1-yl sulphate. In contrast, the arylsulphohydrolase, in common with other similar enzymes previously studied, catalysed the fission of the O-S bond of potassium p-nitrophenyl sulphate.

Detergents↗

PubMed1977

A novel mechanism of enzymic ester hydrolysis. Inversion of configuration and carbon-oxygen bond cleavage by secondary alkylsulphohydrolases from detergent-degrading micro-organisms.

The hydrolysis was studied of potassium (+)-octan-2-yl sulphate by two analogous, optically stereospecific, secondary alkylsulphohydrolases purified from two detergent-degrading micro-organisms, Comamonas terrigena and Pseudomonas C12B. Polarimetry studies have shown that (+)-octan-2-yl sulphate prepared from (+)-octan-2-ol is hydrolysed by both enzymes to yield (-)-octan-2-ol. This inversion of configuration implies that the enzymes are catalysing the scission of the C-O bond of the C-O-S linkage, a type of bond scission apparently not hitherto encountered among hydrolytic enzymes acting on ester bonds. Enzymic hydrolysis of potassium (+)-octan-2-yl sulphate in the presence of H218O and analysis of hydrolysis products for the presence of 18O has confirmed that C-O bond scission (and not O-S bond scission) occurs with both enzymes.

Arylsulfatases↗

PubMed1977