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Characteristics of Alcohol Dehydrogenases of Certain Aerobic Bacteria Representing Human Colonic Flora
Author(s) -
Nosova T.,
JousimiesSomer H.,
Kaihovaara P.,
Jokelainen K.,
Heine R.,
Salaspuro M.
Publication year - 1997
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/j.1530-0277.1997.tb03795.x
Subject(s) - flora (microbiology) , bacteria , aerobic bacteria , microbiology and biotechnology , alcohol , alcohol dehydrogenase , biology , chemistry , biochemistry , genetics
We have recently proposed the existence of a bacteriocolonic pathway for ethanol oxidation [i.e., ethanol is oxidzed by alcohol dehydrogenases (ADHs) of intestinal bacteria resulting in high intracoIonic levels of reactive and toxic acetaldehyde]. The aim of this in vitro study was to characterize further ADH activity of some aerobic bacteria, representing the normal human colonic flora. These bacteria were earlier shown to possess high cytosolic ADH activities ( Escherichia coli IH 133369, Klebsiella pneumoniae IH 35385, Kleb‐siella oxytoca IH 35339, Pseudomonas aeruginosa IH 35342 , and Hafnia ahrei IH 53227 ). ADHs of the tested bacteria strongly preferred NAD as a cofactor. Marked ADH activities were found in all bacteria, even at low ethanol concentrations (1.5 mM) that may occur in the colon due to bacterial fermentation. The K m for ethanol varied from 29.9 mM for K. pneumoniae to 0.06 mM for Hafnia ahrei . The inhibition of ADH by 4‐methylpyrazole was found to be of the competitive type in 4 of 5 bacteria, and K 1 varied from 18.26 ± 3.3 mM for Eschmbhia coli to 0.47 ± 0.13 mM for K. pneumoniae . At pH 7.4, ADH activity was significantly lower than at pH 9.6 in four bacterial strains. ADH of K. oxytoca , however, showed almost equal activities at neutral pH and at 9.6. In conclusion, NAD‐linked alcohol dehydrogenases of aerobic colonic bacteria possess low apparent K m 's for ethanol. Accordingly, they may oxidize moderate amounts of ethanol ingested during social drinking with nearly maximal velocity. This may result in the marked production of intracolonic acetaldehyde. Kinetic characteristics of the bacterial enzymes may enable some of them to produce acetaldehyde even from endogenous ethanol formed by other bacteria via alcoholic fermentation. The microbial ADHs were inhibited by 4‐methylpyrazole by the same competitive inhibition as hepatic ADH, however, with nearly 1000 times lower susceptibility. Individual variations in human colonic flora may thus contribute to the risk of alcohol‐related gastrointestinal morbidity, such as diahea, colon polyps and cancer, and liver injury.