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211.
n-Butane was metabolized in Mycobacterium vaccae (JOB5) via terminal oxidation. This organism metabolized 2-butanone through propionate (or propionyl coenzyme A). Subterminal oxidation in M. vaccae was apparently limited to propane. 相似文献
212.
Structural investigations on the lignin–carbohydrate complexes of Lolium perenne 总被引:5,自引:0,他引:5
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Ian M. Morrison 《The Biochemical journal》1974,139(1):197-204
1. Lignin-carbohydrate complexes isolated from leaf blade, leaf sheath and stem tissue of ryegrass by extraction with dimethyl sulphoxide were examined by fractionation procedures. Although the complexes are heterogeneous, heterogeneity is shown only in the ratio of the individual monosaccharide residues and not in the ratio of lignin to carbohydrate. 2. The molecular weight of the complexes is high (>/=150000), but chemical modification by alkaline hydrolysis, borohydride reduction or lead tetra-acetate oxidation does not drastically decrease it. Low-molecular-weight fragments released by alkaline treatment were shown to contain acetic acid, ferulic acid and p-coumaric acid. 3. On the basis of the chemical stability of the complexes, it is postulated that at least three types of bonding may be present between lignin and carbohydrate, namely one cleaved on borohydride reduction, another cleaved by alkali and a linkage resistant to alkali. 4. The carbohydrate portion of the complexes is composed of beta-(1-->4)-linked d-glucose residues (cellulose) and beta-(1-->4)-linked chains of xylose residues. Side chains involving arabinose and galactose residues are linked to C-3 of some of the xylose residues. 5. How the components of the complexes are held together is not certain, but it is suggested that the phenolic acids may act as cross-linking agents. 相似文献
213.
Affinity chromatography of nicotinamide nucleotide-dependent dehydrogenases on immobilized nucleotide derivatives 总被引:3,自引:3,他引:0
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A series of chemically-defined adenosine phosphate ligands attached to Sepharose 4B were used as active-site probes in studying the interaction of enzymes with their coenzymes and substrates and to test the suitability of these matrices for `general ligand' affinity chromatography. Nicotinamide nucleotide-dependent dehydrogenases were used as models to test this methodology. Elution from these columns by NAD+ and/or AMP gradients (in the presence or the absence of substrates and/or nicotinamide mononucleotide) was consistent with: (1) the compulsory ordered addition of substrates to lactate and malate dehydrogenase; (2) the necessity for the NMN moiety of NAD+ to bind to these enzymes before the substrate; and illustrated: (3) that the binding of these two hydrogenases to these columns compared very well with the published three-dimensional models for these enzymes and (4) that separation of mixtures of dehydrogenases depended on the choice of matrix and displacing ion and whether any additions (e.g. substrates) were made to the gradients used. These techniques were used to purify UDP-glucose dehydrogenase from a crude starting material on a phosphate-linked UDP (or ADP) matrix. The binding of this enzyme to these two columns was not consistent with either an ordered or random addition of substrates and suggested a more complex mechanism. 相似文献
214.
Steady-state kinetics of catecholamine transport by chromaffin-granule `ghosts'' 总被引:9,自引:7,他引:2
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John H. Phillips 《The Biochemical journal》1974,144(2):319-325
Resealed chromaffin-granule ;ghosts' were used to study the steady-state kinetics of catecholamine transport. The pump has a high affinity for (-)-noradrenaline, (-)-adrenaline, tyramine and 5-hydroxytryptamine (serotonin), but a lower affinity for (+)-noradrenaline. The measured rates of incorporation do not conform to Michaelis-Menten kinetics, but affinity constants for the former substrates are in the range 8-18mum. Reserpine is a potent inhibitor. Incorporation as a function of ATP concentration also fails to show simple kinetics; the affinity constant for ATP is deduced to be about 3mm at 1mm-MgCl(2). Adenylyl (betagamma-methylene)diphosphonate is a competitive inhibitor at low concentrations, but inhibits more strongly at high concentrations. The pump has a transition temperature at 29 degrees C and does not seem to be identical with the Mg(2+)-stimulated adenosine triphosphatase of chromaffin granules. 相似文献
215.
A comparison of two methods for fitting the integrated Michaelis–Menten equation (Short Communication) 总被引:1,自引:0,他引:1
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The methods of Atkins & Nimmo (1973) and Fernley (1974) for fitting the integrated Michaelis-Menten equation were compared by using the same sets of simulated experimental data. The method of Fernley (1974) is to be preferred because it gives precise and unbiased estimates of the Michaelis-Menten parameters over a wide range of substrate concentrations. However, the estimates may not be symmetrically distributed, especially at low substrate concentrations. 相似文献
216.
Cyclophosphamide, given in widely spaced doses, was used in the treatment of a patient with pemphigus vulgaris and a patient with bullous pemphigoid. To our knowledge, this form of therapy has not previously been reported in these two diseases. The distinct advantages of the larger intermittent dose method of cyclophosphamide therapy over the more conventional daily dose regimen are discussed. 相似文献
217.
Ian K. Buckley 《Tissue & cell》1974,6(1):1-20
To assess the possible role of filaments in subcellular motility, particular cultured cells were studied by light and electron microscopy. Motile cell margins always contained meshworks of ~50 Å diam. filaments. Organelles moved within cytoplasm occupied by a meshwork of 50–100 Å filaments and microtubules. When cells were treated with cytochalasin B, movements of cell margins stopped, but organelle movements continued; electron microscopically, while subplasmalemmal filaments had disappeared, subcortical filaments and microtubules remained. When cells were treated with hypertonic medium, organelle movements ceased but marginal movements continued; electron microscopically, although cell margins contained normal filament arrays, few subcortical filaments remained. It is concluded that while cell margins are moved by a meshwork of filaments, organelle movement is mediated by a subcortical meshwork of filaments and microtubules. 相似文献
218.
A.Ian Scott L.C. Beadling N.H. Georgopapadakou C.R. Subbarayan 《Bioorganic chemistry》1974,3(2):238-248
6-MSA3 synthase has been purified 190-fold with 33% yield. The purification was found to be dependent on the presence of glycerol. The acetylenic inhibitors 3-pentynoyl- and 2-hexynoyl-NAC completely inhibit 6-MSA production at concentrations in which fatty acid synthesis, TAL production as well as NADPH oxidation are only partially affected. These results confirm earlier studies on the specificity of inhibition by acetylenic inhibitors and support a mechanism wherein the NADPH-mediated reduction step occurs on a 6-carbon rather than on an 8-carbon intermediate. 相似文献
219.
Kinetic and molecular properties of citraconyl-aldolase. The reversible denaturation and hybridization of the native and modified enzymes 总被引:5,自引:5,他引:0
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1. The preparation of enzymically active N-citraconyl derivatives of fructose diphosphate aldolase from rabbit muscle is described. Reaction is restricted to amino groups and the derivatives are not very heterogeneous with respect to the number of substituents. 2. Linear double-reciprocal plots of enzyme velocity against substrate concentration are found up to about 15% blocking of amino groups. With more than 15% blocking, there is a marked downward curvature in the double-reciprocal plots at high substrate concentrations. 3. Over the range 0-25% blocking of amino groups the apparent V(max.) for fructose diphosphate falls to 10% that of the native enzyme, and the apparent K(m) rises from 1 to 400mum. 4. Various pieces of evidence suggest that citraconyl-aldolase is slightly distorted in structure compared with the native enzyme. However, the kinetic properties and tetrameric structure of citraconyl-aldolase can be completely recovered after denaturation in 4m-guanidine hydrochloride. 5. After removal of the citraconyl groups in acid conditions the kinetic and molecular properties of native enzyme are restored. 6. Hybrid forms of aldolase can be constructed containing native and citraconylated subunits and the suitability of these derivatives for the study of subunit interactions in the enzyme is discussed. 7. The kinetic properties of hybridized aldolase containing native and citraconylated subunits are not exactly those predicted from the kinetic properties of the two parental forms. This result is interpreted in terms of conformational changes induced in the native and modified subunits when both are present in a hybrid molecule, evidently as a result of interactions in the tetramer. 相似文献
220.
John H. Phillips 《The Biochemical journal》1974,144(2):311-318
A method is described for the preparation of resealed chromaffin-granule ;ghosts'. The lysis and rapid purification procedures provide ;ghosts' in approximately 70% yield from crude granules; the preparation contains 0.1mumol of catecholamine/mg of protein (as compared with 2.8mumol/mg in unlysed granules), of which about one third is inside the ;ghosts'. The ;ghosts' retain their ability to accumulate catecholamines, a process dependent on Mg-ATP and inhibited by reserpine, and a simple assay for this transport is described. 相似文献