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112.
Lars Anderson Per Hägglund Dominik Stoll Leila Lo Leggio Torbjörn Drakenberg 《Biocatalysis and Biotransformation》2013,31(1-2):86-95
Endo–1,4-β-mannanases (β-mannanases) randomly hydrolyse the mannosidic bonds within the main chain of various mannans and heteromannans. Some of these polysaccharides are hemicelluloses, a major part of the plant cell-wall. The β-mannanases have been assigned to family 5 and 26 of the glycoside hydrolase clan A. This work presents a detailed kinetic analysis of the family 26 β-mannanase CfMan26A from the soil-bacterium Cellulomonas fimi. The full-length enzyme consists of five modules: a family 26 catalytic module, an immunoglobulin-like module, a mannan-binding module, a surface layer homology-module and a module of unknown function. A truncated variant consisting of the catalytic module and the immunoglobulin-like module was used in these studies. The degradation of mannotriose, mannotetraose and mannopentaose was studied by 1H-NMR. First, the mutarotation of one of the hydrolysis products (mannose) was determined to be 1.7 10?5s?1 at 5°C and pH 5.0. As expected for a family 26 glycoside hydrolase, the hydrolysis was shown to proceed with overall retention of the anomeric configuration. Many ‘retaining’ enzymes can perform transglycosylation reactions. However, no transglycosylation could be detected. Kinetic constants were calculated from progress curves using computer simulation. It was revealed that the ?3 subsite had a greater impact on the apparent kcat/Km ratio (the catalytic efficiency) than the +2 subsite. The β-anomer of mannotriose was hydrolysed 1000-times more efficiently than the α-anomer indicating selectivity for the β- over the α-anomer in the +1 subsite. With background information from the previous published 3D-structure of the truncated variant of Man26A, a structural explanation for the observations is discussed. 相似文献
113.
Jerzy Kączkowski 《Acta Physiologiae Plantarum》2003,25(3):287-305
The review concerns the newer aspects of plant cell wall construction and modification, including the structure and biosynthesis
of basic components during the cell growth and differentiation, as well as their breakdown. The special interest is given
to the enzymes incorporated into the cell wall and their specific activity in the biosynthesis and degradation processes,
but also in the transfer of glycosyl fragments (blocks), which is connected with its thickening, softening, constructing the
channels a.o. New aspects of lignification and specialisation of particular wall fragments, playing various functions, such
as fruit ripening, dropping down leaves, fruits and flowers, breaking the dormancy, and others, are also presented. 相似文献