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  • 1
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Excursion temperature dependences of spectral hole profiles in photochemical hole burning for free-base systems porphyrin/poly(alkyl methacrylate)s are investigated to see the relationship between relaxation properties and chemical structure of the polymers. The irreversible change in hole width is a characteristic of each polymer and is very similar to the relaxation behavior measured mechanically and dielectrically. Poly(methyl methacrylate) (PMMA) shows the highest thermal stability of hole profiles among the polymers presently studied with no marked appearance of local relaxation at 20-100 K. Poly(ethyl methacrylate) (PEMA) and poly(isopropyl methacrylate) (PiPMA) show an increase in hole width even at 20 K with a plateau region at 50-70 K, which is attributed to the rotation of the ethyl or isopropyl group around the C—O bond. Polymers which contain more than two serial methylene groups in the side chains (poly(propyl methacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate)) show a similar relaxation behavior around 50-60 K, suggesting the onset of the rotation of the terminal ethyl or isopropyl group in the ester side chain around the C—C bond. Low-density polyethylene (LDPE) shows a similar excursion-temperature dependence probably due to the existence of branched oligomethylene side chains. The relaxation behavior is independent of the nature of chromophores, which indicates that irreversible hole broadening is controlled mainly by the local motion of the host matrices.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2018-06-02
    Description: Bacillus thuringiensis Cry toxins are insecticidal proteins used widely for pest control. They are lethal to a restricted range of insects via specific interactions with insect receptors such as the ABC transporter subfamily members C2 (ABCC2) and C3 (ABCC3). However, it is still unclear how these different receptors contribute to insect susceptibility to Cry1A toxins. Here, we investigated the differences between the silkworm (Bombyx mori) ABCC2 (BmABCC2_S) and ABCC3 (BmABCC3) receptors in mediating Cry toxicity. Compared with BmABCC2_S, BmABCC3 exhibited 80- and 267-fold lower binding affinities to Cry1Aa and Cry1Ab, respectively, and these decreased affinities correlated well with the lower receptor activities of BmABCC3 for these Cry1A toxins. To identify the amino acid residues responsible for these differences, we constructed BmABCC3 variants containing a partial amino acid replacement with extracellular loops (ECLs) from BmABCC2_S. Replacing three amino acids from ECL 1 or 3 increased BmABCC3 activity toward Cry1Aa and enabled its activity toward Cry1Ab. Meanwhile, BmABCC2_S and BmABCC3 exhibited no receptor activities for Cry1Ca, Cry1Da, and Cry3Bb, correlating with markedly lower binding affinities for these Cry toxins. ABCC2 from a Cry1Ab-resistant B. mori strain (BmABCC2_R), which has a tyrosine insertion in ECL 2, displayed 93-fold lower binding affinity to Cry1Ab compared with BmABCC2_S but maintained high binding affinity to Cry1Aa. These results indicate that the Cry toxin–binding affinities of ABCC transporters are largely linked to the level of Cry susceptibility of ABCC-expressing cells and that the ABCC ECL structures determine the specificities to Cry toxins.
    Print ISSN: 0021-9258
    Electronic ISSN: 1083-351X
    Topics: Biology , Chemistry and Pharmacology
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