Biochemical, molecular and physiological characterization of 1-butanol dehydrogenases of Pseudomonas butanovora in butane and 1-butanol metabolism
| Autor: | Vangnai, Alisa S. |
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| Rok vydání: | 2002 |
| Předmět: | |
| Druh dokumentu: | Thesis/Dissertation |
| Popis: | Butane-grown Pseudomonas butanovora oxidized butane by a soluble butane monooxygenase through the terminal pathway yielding 1 -butanol as the predominant product. Alcohol dehydrogenases (ADHs) involved in butane oxidation in P. butanovora were purified and characterized at the biochemical, genetic and physiological levels. Butane-grown P. butanovora expressed a type I soluble quinoprotein 1 -butanol dehydrogenase (BOH), a soluble type II quinohemoprotein 1 -butanol dehydrogenase (BDH) and an NAD���-dependent secondary ADH. Two additional NAD���-dependent secondary ADHs were also detected in cells grown on 2-butanol and lactate. BDH was purified to near homogeneity and characterized. BDH is a monomer of 66 kDa consisting of one mole of pyrroloquinoline quinone (PQQ) and 0.25 mole of heme c as the prosthetic groups. BOH was partially purified and its deduced amino acid sequence suggests a 67-kDa ADH containing a PQQ as a cofactor. BOH and BDH exhibited high activities and preference towards I -butanol and fair preference towards butyraldehyde. While BDH could not oxidize 2-butanol, BOH is capable of 2-butanol oxidation and has a broader substrate range than that of BDH. Genes encoding BOH and BDH and their deduced amino acid sequences were identified. BOH and BDH mRNAs and 1-butanol oxidation activity were induced when cells were exposed to butane. Primary C��� and C��� alcohols were the most effective inducers for boh and bdh. Some secondary alcohols, such as 2-butanol, were also inducers for BOH mRNA, but not for BDH mRNA. Insertional inactivation of boh or bdh affected unfavorably, but did not eliminate, butane utilization in P. butanovora. The P. butanovora mutant strain with both boh and bdh genes disrupted was unable to grow on butane and 1-butanol. This result confirmed the involvement of BOH and BDH in butane and 1-butanol metabolism in P. butanovora. Roles of B011 and BDH in butane and 1-butanol metabolism were further studied at the physiological level. There are no substantial differences between BOH and BDH in the mRNA expressions in response to three different 1- butanol levels tested and in their abilities to respond to 1-butanol toxicity. Different bioenergetic roles of BOH and BDH in butane and 1-butanol metabolism were suggested. A model of 1 -butanol- dependent respiratory systems was proposed where the electrons from 1 -butanol oxidation follow a branched electron transport chain. The role of BOH was suggested to function primarily in energy generation because B011 may couple to ubiquinone with the electrons being transported to a cyanide-sensitive terminal oxidase. BDH may be more important in the detoxification of 1 -butanol because the electrons from BDH may be transferred to a terminal oxidase system that is less sensitive to cyanide, which is not capable of energy generation. Graduation date: 2003 |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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