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Biomedical subjects

I C Hancock

Publications and source records attributed to I C Hancock.

34 records · Page 2Linked to original sources
PubMed1978

The enzymic synthesis of beta-[32P]UDP-N-acetylglucosamine.

Cells of Micrococcus sp. 2102 incorporate inorganic [32P]phosphate from the medium into the sugar-phosphate polymer of the wall. Controlled acid hydrolysis of sodium dodecyl sulphate-extracted cells gives N-acetylglucosamine 6-[32P]-phosphate which can be purified by ion-exchange chromatography and incubated with UTP in the presence of crude preparations of phosphoacetylglucosamine mutase from Neurospora crassa and UTP:N-acetylglucosamine 1-phosphate phosphotransferase from Bacillus licheniformis which act in concert to synthesise beta-[32P]UDP-N-acetylglucosamine.

Acetylglucosamine↗
PubMed1977

Occurrence and function of membrane teichoic acids.

Membrane teichoic acids, sometimes described as lipoteichoic acids, are important but not major components of nearly all Gram-positive bacteria. They appear on the outer surface of the cytoplasmic membrane and possess antigenic properties. Several functions have been ascribed to these glycerol phosphate polymers, including the binding of divalent cations required for optimal activity of membrane-bound enzymes, and the control of certain lytic enzymes. A substance that is identical or closely similar to membrane teichoic acid, lipoteichoic acid carrier, plays an important part in the biosynthesis of wall teichoic acid; it accepts polyol phosphate residues from CDP-glycerol or CDP-ribitol to form a polyol phosphate chain which is then transferred after the incorporation of a tri(glycerol phosphate) linkage unit, to the growing glycan chain of peptidoglycan.

Bacillus subtilis↗
PubMed1975

The interaction of magnesium ions with teichoic acid.

The binding of Mg2+ to the wall teichoic acid of Lactobacillus buchneri N.C.I.B. 8007 was measured by equilibrium dialysis at controlled ionic concentration and pH. In an aqueous solution containing 10mM-NaCl at pH 5.0 one Mg2+ ion was bound for every two phosphate groups of the teichoic acid, with an apparent association constant, Kassoc. = 2.7 x 10(3) M-1. On lowering the pH below the pKa of the phosphate groups the amount of bound Mg2+ decreased concomitantly with decreasing ionization of the phosphate groups. Both the amount of Mg2+ bound to the teichoic acid and the apparent association constants were similar in the presence of 10 mM concentrations of NaCl or KCl but decreased markedly in the presence of 10 mM-CaCl2 because of competition between Ca2+ and Mg2+ for the binding sites. A similar effect was found when the concentration of NaCl was increased from 0 to 50 mM. The results are discussed in relation to the function of teichoic acid in the walls of Gram-positive bacteria.

Binding Sites↗
PubMed1975

Influence of alanyl ester residues on the binding of magnesium ions to teichoic acids.

The binding of Mg2+ to the ribitol teichoic acid of Staphylococcus aureus H walls was examined by equilibrium dialysis in solution and in the intact wall; the influence of alanyl ester groups on binding was determined. In solution the ribitol polymer had a lower affinity than did a glycerol teichoic acid and bound Mg2+ in the ratio Mg2+/P of 1:1. The presence of alanyl ester residues caused a decrease in the amount of cations bound in stoicheiometric proportion to the ratio Ala/P, but the affinity constant was unaltered. It is concluded that in solution the ribitol teichoic acid binds Mg2+ univalently to phosphate groups and univalently to a counter-ion. In the intact wall the binding of Mg2+ was different. The affinity constant was higher and resembled that of a glycerol teichoic acid. It is concluded that Mg2+ forms bridges across phosphate groups in teichoic acid chains lying adjacent to each other in the wall. The effect of alanyl esters was similar to that in solution, but Scatchard plots were not linear at low concentrations of Mg2+ where it was shown that the difference in affinities between walls with and without alanyl ester residues was much greater than it was at higher concentrations of Mg2+. Thus at very low concentrations of Mg2+ effective binding to the wall is markedly improved by loss of alanyl ester residues.

Alanine↗
PubMed1973

The function of teichoic acids in cation control in bacterial membranes.

1. The effects of teichoic acids on the Mg(2+)-requirement of some membrane-bound enzymes in cell preparations from Bacillus licheniformis A.T.C.C. 9945 were examined. 2. The biosynthesis of the wall polymers poly(glycerol phosphate glucose) and poly(glycerol phosphate) by membrane-bound enzymes is strongly dependent on Mg(2+), showing maximum activity at 10-15mm-Mg(2+). 3. When the membrane is in close contact with the cell wall and membrane teichoic acid, the enzyme systems are insensitive to added Mg(2+). The membrane appears to interact preferentially with the constant concentration of Mg(2+) that is bound to the phosphate groups of teichoic acid in the wall and on the membrane. When the wall is removed by the action of lysozyme the enzymes again become dependent on an external supply of Mg(2+). 4. A membrane preparation that retained its membrane teichoic acid was still dependent on Mg(2+) in solution, but the dependence was damped so that the enzymes exhibited near-maximal activity over a much greater range of concentrations of added Mg(2+); this preparation contained Mg(2+) bound to the membrane teichoic acid. The behaviour of this preparation could be reproduced by binding membrane teichoic acid to membranes in the presence of Mg(2+). Addition of membrane teichoic acid to reaction mixtures also had a damping effect on the Mg(2+) requirement of the enzymes, since the added polymer interacted rapidly with the membrane. 5. Other phosphate polymers behaved in a qualitatively similar way to membrane teichoic acid on addition to reaction mixtures. 6. It is concluded that in whole cells the ordered array of anionic wall and membrane teichoic acids provides a constant reservoir of bound bivalent cations with which the membrane preferentially interacts. The membrane teichoic acid is the component of the system which mediates the interaction of bound cations with the membrane. The anionic polymers in the wall scavenge cations from the medium and maintain a constant environment for the membrane teichoic acid. Thus a function of wall and membrane teichoic acids is to maintain the correct ionic environment for cation-dependent membrane systems.

Bacillus↗
PubMed1972

Biosynthesis of the wall teichoic acid in Bacillus licheniformis.

1. The biosynthesis of the wall teichoic acid, poly(glycerol phosphate glucose), has been studied with a particulate membrane preparation from Bacillus licheniformis A.T.C.C. 9945. The precursor CDP-glycerol supplies glycerol phosphate residues, whereas UDP-glucose supplies only glucose to the repeating structure of the polymer. 2. Synthesis proceeds through polyprenol phosphate derivatives, and chemical studies and pulse-labelling techniques show that the first intermediate is the phosphodiester, glucose polyprenol monophosphate. CDP-glycerol donates a glycerol phosphate residue to this to give a second intermediate, (glycerol phosphate glucose phosphate) polyprenol. 3. The glucose residue in the lipid intermediates has the beta configuration, and chain extension in the synthesis of polymer occurs by transglycosylation with inversion of anomeric configuration at two stages.

Bacillus↗