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Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. Increasingly, raw materials such as crude oil are in short supply for the synthesis of plastics, and the recycling of waste plastics is becoming more important. As the importance of recycling increases, so do studies on elucidation of the biodegradability of polyurethanes. Polyurethanes are an important and versatile class of man-made polymers used in a wide variety of products in the medical, automotive and industrial fields. Polyurethane is a general term used for a class of polymers derived from the condensation of polyisocyanates and polyalcohols. Despite its xenobiotic origins, polyurethane has been found to be susceptible to biodegradation by naturally occurring microorganisms. Microbial degradation of polyurethanes is dependent on the many properties of the polymer such as molecular orientation, crystallinity, cross-linking and chemical groups present in the molecular chains which determine the accessibility to degrading-enzyme systems. Esterase activity (both membrane-bound and extracellular) has been noted in microbes which allow them to utilize polyurethane. Microbial degradation of polyester polyurethane is hypothosized to be mainly due to the hydrolysis of ester bonds by these esterase enzymes. 相似文献
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The gorgoniid Eugorgia is exclusively an eastern Pacific genus. It has a wide geographic and bathymetric range of distribution, found from California to Perú and extends down to 65 m deep. Two new species are herein described. The morphological characters were analyzed and illustrated by light and scanning electron microscopy. Eugorgia beebei
sp. n. can be distinguished by its white, ascending, sparse colony growth. Eugorgia mutabilis
sp. n. can be distinguished by its white colony that changes color after collection, and the conspicuous sharp-crested disc sclerites. From a morphological point of view the new species are related to the daniana-group, the rubens-group and the siedenburgae-group of Eugorgia; their affiliations, and the proposal of a new group are discussed. These new species increases the number of species in the genus to 15, and contribute to the knowledge of the eastern Pacific octocoral biodiversity. 相似文献
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Molecular and Cellular Biochemistry - 相似文献
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Nimra Khan Dylan Pelletier Thomas S. McAlear Nathalie Croteau Simon Veyron Andrew N. Bayne Corbin Black Muneyoshi Ichikawa Ahmad Abdelzaher Zaki Khalifa Sami Chaaban Igor Kurinov Gary Brouhard Susanne Bechstedt Khanh Huy Bui Jean-François Trempe 《Structure (London, England : 1993)》2021,29(6):572-586.e6
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Posner , Herbert B., and William S. Hillman . (Yale U., New Haven, Conn.) Effects of x irradiation on Lemna perpusilla. Amer. Jour. Bot. 47(6): 506–511. Illus. 1960.—The effects of x rays on the multiplication rates (MR), percent flowering (Fl%) and gross morphology of aseptically grown cultures of Lemna perpusilla, strain 6746, were studied. MR values are unaffected by doses of less than 300 r but are progressively depressed as the dose increases. The effect of a given dose on short-term MR values is the same at the 2 dosage intensities used, 500 and 2000 r/min. The inhibitory effect of intermediate doses on long-term growth is delayed; high doses have an “immediate” effect. Bleaching of fronds and cessation of growth occur in all cultures given 5,000 r or higher. Radiosensitivity is not altered by addition of yeast extract and casein hydrolysate to the medium. Depressed Fl% and seed production appear to be consequences of lowered MR. Morphological aberrations such as small size, epinasty and wrinkling are temporary. Frond-sequence may be altered by x rays but this aberration is permanent. Various aspects of the results are discussed. 相似文献