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  • Polymer and Materials Science  (3)
  • dynamic light scattering  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Size distribution and photophosphorylation of chromatophores from t Rhodospirillum rubrum (1997)
    Springer
    Photosynthesis research 51 (1997), S. 51-59 
    Details
    ISSN: 1573-5079
    Keywords: aggregation ; dynamic light scattering ; hydrodynamic diameter ; 31P-NMR ; t R. rubrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Morphology and photophosphorylation of chromatophores from t Rhodospirillum rubrum have been investigated by dynamic light scattering (DLS) and in situ 31P-NMR measurement. Two components, designated as light and heavy fractions, with different average sizes and size distributions were detected by the DLS and can be separated by sucrose density gradient centrifugation. The light fraction has an average size of about 140 nm in diameter with a narrow distribution and shows a high activity of photophosphorylation. About 70 of ADP were found to be converted to ATP purely by the photophosphorylative reaction. In contrast, the heavy fraction has a broad size distribution centered around 350 nm and a low activity of photophosphorylation. Only about 50 of ADP was converted into ATP and AMP with a ratio of 7:3, indicating that most membrane-bound adenylate kinase are attached on the particles of the heavy fraction. Effect of physical disruption on the structural integrity of chromatophores has been examined by using sonication with various oscillating strengths. The result shows that the morphology of chromatophores for both light and heavy fractions is relatively stable to the disruption, while the photophosphorylative activity of the light fraction is very sensitive to the disrupting strength, suggesting that the internal structure of the purified chromatophores could be partially damaged by the disruption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005788528069
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  • 2
    Electronic Resource
    Electronic Resource
    Interaction of amylose and other α-glucans with hydrophobic fluorescent probe (2-p-toluidinylnaphthalene-6-sulfonate) (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 2363-2370 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fluorescence of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) was enhanced in the presence of maltooligosaccharides, amylose, and other α-glucans. The dependence of relative TNS fluorescence intensity per glucose unit on chain length of oligosaccharides was examined. The values of binding constant and thermodynamic parameters, assuming the 1:1 complex for TNS-amylose (number-average degree of polymerization, DPN = 17), were determined by the fluorescence titration. The values of thermodynamic parameters for 1:1 complex formation of TNS-α- and β-cyclodextrins were also determined and compared with those of TNS-amylose (DPN = 17). The fluorescence intensity of TNS in the presence of amylose (DPN = 600) decreased by the action of glucoamylase and taka-amylase A. The fluorescence of TNS-amylose (DPN = 17) system increased with the increased ionic strength. In the presence of pullulan, TNS fluorescence was also enhanced and decreased by the action of pullulanase. Amylopectin enhanced TNS fluorescence rather more strongly than amylose (DPN = 17) at the same concentration. In the presence of dextran, the fluorescence of TNS was scarcely enhanced. The degree of fluorescence enhancement of TNS in the presence of α-glucans seems to reflect the structures of α-glucans in solution, since TNS fluorescence is enhanced in the hydrophobic environment or by the disturbance of free intramolecular rotation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360161103
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of multiple attack mechanism of α-amylase (1996)
    New York : Wiley-Blackwell
    Biopolymers 39 (1996), S. 665-669 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Porcine pancreatic α-amylase (EC 3.2.1.1) produces short maltooligosaccharides from a single enzyme-substrate complex without dissociation by multiple or repetitive attack. Multiple attack is caused by relative sliding of the enzyme along the product chain of the enzyme-product complex without dissociation to form another productive complex. The Monte Carlo method was applied to the multiple attack mechanism to predict product distribution from amylose and amylopectin molecules of arbitrary sizes. The position of the initial attack to make the enzyme-substrate complex and branched reaction paths from the enzyme-product complex were selected by random numbers and probabilities. A simulated product distribution from 100,000 samples of amylose of chain length greater than 80 agreed completely with experimental data at the early stage of hydrolysis of amylose of mean chain length 90. On the other hand, the simulated product distribution from amylopectin agreed with experimental data of potato amylopectin when the effective chain length of the A chain was 9. Since the mean chain length of the A chain of potato amylopectin is 15, it is possible that amylopectin is partially compact in solution, so that the enzyme can recognize and act only on the outer side of the A chain at the early stage of digestion. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of multiple attack mechanism of β-amylase-catalyzed reaction (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 831-836 
    Details
    ISSN: 0006-3525
    Keywords: β-amylase ; sweet potato ; multiple attack ; Monte Carlo ; computer simulation ; enzyme mechanism ; enzyme kinetics ; maltooligosaccharides ; random walk model ; statistical method ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Amylase (EC 3.2.1.2) produces maltose (dimer) from the nonreducing ends of α-1,4 glucosidic bonds of substrates like maltooligosaccharides, amylose, and amylopectin. The enzyme releases several maltose molecules from a single enzyme-substrate complex without dissociation by multiple or repetitive attack containing many branching reaction paths. The Monte Carlo method was applied to the simulation of the β-amylase-catalyzed reaction including the multiple attack mechanism. The simulation starts from a single enzyme molecule and a finite number of substrate molecules. The selection of the substrate by the enzyme and degree of multiple attack proceeds by random numbers produced from a computer. The simulation was carried out until the whole substrate and the intermediate molecules were consumed. The simulated data were compared with experimental data of sweet potato β-amylase using heptamer, octamer, nanomer, and 11-mer as substrates. The only adjustable parameter for odd-numbered substrates was the probability of multiple attack, while an additional adjustable parameter (a correction factor due to low reactivity of tetramer) was needed for even-numbered substrates. © 1997 John Wiley & Sons, Inc. Biopoly 42: 831-836, 1997
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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