ISSN:
1432-072X
Keywords:
Methanogenic bacteria
;
Alcohols
;
Ketones
;
Aldehydes
;
Alcohol dehydrogenase
;
Enzyme expression
;
Methanogenium thermophilum
;
Factor F420
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In four species of methanogens able to grow with secondary alcohols as hydrogen donors the expression and properties of secondary alcohol dehydrogenase (sec-ADH) were investigated. Cells grown with 2-propanol and CO2 immediately started to oxidize secondary alcohols to ketones if transferred to new media. In the presence of H2, such cells reduced ketones or aldehydes to alcohols. In the absence of H2, aldehydes were dismutated (without growth) to primary alcohols and fatty acids. None of these reactions was catalyzed by cells grown with only H2 and CO2 at non-limiting concentration. This indicated an induction or derepression of sec-ADH by its substrate. Apparently, sec-ADH in all strains enabled not only the reduction of ketones or aldehydes, but also the dismutation of the latter. Sec-ADH was also expressed if strains were grown on H2 and CO2 in the presence of non-oxidizable, tertiary alcohols. Methanogenium thermophilum expressed sec-ADH even without added alcohol when H2 became limiting. From this species, an F420-specific sec-ADH was purified; the final gel filtration chromatography yielded a single protein peak that coincided with the activity. The enrichment was 12-fold, the activity recovery 26%. SDS polyacrylamide gel electrophoresis indicated that the enzyme was a homodimer with an apparent M r of 79,000. At the pH optimum around 4.2, the specific activity for oxidation of 2-propanol (130 mM) and reduction of acetone (20 mM) was 176 and 110 μmol/ min·mg, respectively (40°C). The apparent K m for 2-propanol and acetone (with 15 μM F420) was 2.5 and 0.25 mM, respectively. Aldehydes also were reduced.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00425168
