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KMID : 0545120070170111789
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Journal of Microbiology and Biotechnology
2007 Volume.17 No. 11 p.1789 ~ p.1796
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Molecular Orbital Theory on Cellulolytic Reactivity Between pNP-Cellooligosccharides and β-Glucosidase from Cellulomonas uda CS1-1
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Yoon Min-Ho
Nam Yun-Kyu
Choi Woo-Young
Sung Nack-Do
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Abstract
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A β-glucosidase with the molecular mass of 160,000 Da was purified to homogeneity from cell extract of a cellulolytic bacterium, Cellulomonas uda CS1-1. The kinetic parameters (Km and Vmax) of the enzyme were determined with pNP-cellooligosccharides (DP 1-5) and cellobiose. The molecular orbital theoretical studies on the cellulolytic reactivity between the pNP-cellooligosaccharides as substrate (S) molecules and the purified β-glucosidase (E) were conducted by applying the frontier molecular orbital (FMO) interaction theory. The results of the FMO interaction between E and S molecules verified that the first stage of the reaction was induced by exocyclic cleavage, which occurred in an electrophilic reaction based on a strong charge-controlled reaction between the highest occupied molecular orbital (HOMO) energy of the S molecule and the lowest occupied molecular orbital (LUMO) energy of the hydronium ion (H3O+), more than endocyclic cleavage, whereas a nucleophilic substitution reaction was induced by an orbital-controlled reaction between the LUMO energy of the oxonium ion (SH+) protonated to the S molecule and the HOMO energy of the H2O2 molecule. A hypothetic reaction route was proposed with the experimental results in which the enzymatic acid-catalyst hydrolysis reaction of E and S molecules would be progressed via SN1 and SN2 reactions. In addition, the quantitative structure-activity relationships (QSARs) between these kinetic parameters showed that Km has a significant correlation with hydrophobicity (logP), and specific activity has with dipole moment, respectively
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KEYWORD
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Cellulolytic reactivity, Cellulomonas uda CS1-1, β-glucosidase, pNP-β-cellooligosaccharides, MO theory
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