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Enzymatic oxidation of ethanol in the gaseous phase
Author(s) -
Barzana Eduardo,
Karel Marcus,
Klibanov Alexander M.
Publication year - 1989
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260340908
Subject(s) - chemistry , thermostability , ethanol , catalysis , aqueous solution , substrate (aquarium) , aqueous two phase system , alcohol oxidase , michaelis–menten kinetics , activation energy , alcohol , kinetics , enzyme catalysis , organic chemistry , inorganic chemistry , enzyme , enzyme assay , biochemistry , pichia pastoris , recombinant dna , oceanography , gene , geology , physics , quantum mechanics
The enzymatic conversion of gaseous substrates represents a novel concept in bioprocessing. A critical parameter in such systems is the water activity, A w The present article reports the effect of A w on the catalytic performance of alcohol oxidase acting on ethanol vapors. Enzyme activity in the gas‐phase reaction increases several orders of magnitude, whereas the thermostability decreases drastically when A w is increased from 0.11 to 0.97. The enzyme is active on gaseous substrates even at hydration levels below the monolayer coverage. Enhanced thermostability at lower hydrations results in an increase in the optimum temperature of the gas‐phase reaction catalyzed by alcohol oxidase. The apparent activation energy decreases as A w increases, approaching the value obtained for the enzyme in aqueous solution. The formation of a pread‐sorbed ethanol phase on the surface of the support is not a prerequisite for the reaction, suggesting that the reaction occurs by direct interaction of the gaseous substrate with the enzyme. The gas‐phase reaction follows Michaelis–Menten kinetics, with a K m value almost 100 times lower than that in aqueous solution. Based on vapor–liquid equilibrium data and observed K m values, it is postulated that during the gas‐phase reaction the ethanol on the enzyme establishes an equilibrium with the ethanol vapor similar to that between ethanol in water and ethanol in the gas phase.