Diacetyl (acetoin) reductase from Aerobacter aerogenes. Structural properties

Properties of diacetyl (acetoin) reductase from Bacillus stearothermophilus

The cells of Bacillus stearothermophilus contain an NADH-dependent diacetyl (acetoin) reductase. The enzyme was easily purified to homogeneity, partially characterised, and found to be composed of two subunits with the same molecular weight. In the presence of NADH, it catalyses the stereospecific reduction of diacetyl first to (3S)-acetoin and then to (2S,3S)-butanediol; in the presence of NAD+, it catalyses the oxidation of (2S,3S)- and meso-butanediol, respectively, to (3S)-acetoin and to (3R)-acetoin, but is unable to oxidise these compounds to diacetyl. The enzyme is also able to catalyse redox reactions involving some endo-bicyclic octen- and heptenols and the related ketones, and its use is suggested also for the recycling of NAD+ and NADH in enzymatic redox reactions useful in organic syntheses.

Purification, characterization and some properties of diacetyl(acetoin) reductase from Enterobacter aerogenes

A new method, faster, milder and more efficient than the one previously described [Bryn, K., Hetland, O. & Stormer, F. C. (1971) Eur. J. Biochem, 18, 116-119], for purification of diacetyl(acetoin) reductase from Enterobacter aerogenes is proposed. The experiments carried out with the electrophoretically pure preparations obtained by this procedure show that the enzyme (a) produces L-glycols from the corresponding L-alpha-hydroxycarbonyls by reversible reduction of their oxo groups and also reduces the oxo group of uncharged alpha-dicarbonyls converting them into L-alpha-hydroxycarbonyls, and (b) is specific for NAD. This is a new enzyme for which we suggest the systematic name of L-glycol: NAD+ oxidoreductase and the recommended name of L-glycol dehydrogenase(NAD). The molecular mass, pI, affinity for substrates and pH profiles of this enzyme are also described.

Purification and characterization of a (R)-2,3-butanediol dehydrogenase from Saccharomyces cerevisiae

A NAD-dependent (R)-2,3-butanediol dehydrogenase (EC 1.1.1.4), selectively catalyzing the oxidation at the (R)-center of 2,3-butanediol irrespective of the absolute configuration of the other carbinol center, was isolated from cell extracts of the yeast Saccharomyces cerevisiae. Purification was achieved by means of streptomycin sulfate treatment, Sephadex G-25 filtration, DEAE-Sepharose CL-6B chromatography, affinity chromatography on Matrex Gel Blue A and Superose 6 prep grade chromatography leading to a 70-fold enrichment of the specific activity with 44% yield. Analysis of chiral products was carried out by gas chromatographic methods via pre-chromatographic derivatization and resolution of corresponding diastereomeric derivatives. The enzyme was capable to reduce irreversibly diacetyl (2,3-butanediol) to (R)-acetoin (3-hydroxy-2-butanone) and in a subsequent reaction reversibly to (R,R)-2,3-butanediol using NADH as coenzyme. 1-Hydroxy-2-ketones and C5-acyloins were also accepted as substrates, whereas the enzyme was inactive towards the reduction of acetone and dihydroxyacetone. The relative molecular mass (Mr) of the enzyme was estimated as 140,000 by means of gel filtration. On SDS-polyacrylamide gel the protein decomposed into 4 (identical) subunits of Mr 35,000. Optimum pH was 6.7 for the reduction of acetoin to 2,3-butanediol and 7.2 for the reverse reaction.

Purification and characterization of diacetyl-reducing enzymes from Staphylococcus aureus

A method was developed to purify diacetyl-reducing enzymes from Staphylococcus aureus. Two enzymes capable of catalysing diacetyl reduction were isolated, neither of which turned out to be a specific diacetyl reductase. One of them is a lactate dehydrogenase similar to the one from Staphylococcus epidermidis, which accepts diacetyl, although poorly. The other one uses as coenzyme beta-NAD and reduces uncharged alpha-dicarbonyls with more than three carbon atoms (especially the alpha-diketones diacetyl and pentane-2,3-dione), producing the L(+) form of the corresponding alpha-hydroxycarbonyls. This enzyme has an Mr of 68,000 and is, most probably, a monomer. Its optimum pH is 6.0. Its shows a high affinity for NADH and a rather low one for diacetyl, which, at least in vitro, does not seem to be as good a substrate as pentane-2,3-dione. We propose for it the systematic name L-alpha-hydroxyketone:NAD+ oxidoreductase and the recommended name of alpha-diketone reductase (NAD). We also suggest that the diacetyl reductase entry in the I.U.B. classification be suppressed.

A multifunctional fermentative alcohol dehydrogenase from the strict aerobe Alcaligenes eutrophus: purification and properties

A NAD (P)-linked alcohol dehydrogenase was isolated from the soluble extract of the strictly respiratory bacterium Alcaligenes eutrophus N9A. Derepression of the formation of this enzyme occurs only in cells incubated under conditions of restricted oxygen supply for prolonged times. The purification procedure included precipitation by cetyltrimethylammonium bromide and ammonium sulfate and subsequent chromatography on DEAE-Sephacel, Cibacron blue F3G-A Sepharose and thiol-Sepharose. The procedure resulted in a 120-fold purification of a multifunctional alcohol dehydrogenase exhibiting dehydrogenase activities for 2,3-butanediol, ethanol and acetaldehyde and reductase activities for diacetyl, acetoin and acetaldehyde. During purification the ratio between 2,3-butanediol dehydrogenase and ethanol dehydrogenase activity remained nearly constant. Recovering about 20% of the initial 2,3-butanediol dehydrogenase activity, the specific activity of the final preparation was 70.0 U X mg protein-1 (2,3-butanediol oxidation) and 2.8 U X mg protein-1 (ethanol oxidation). The alcohol dehydrogenase is a tetramer of a relative molecular mass of 156000 consisting of four equal subunits. The determination of the Km values for different substrates and coenzymes as well as the determination of the pH optima for the reactions catalyzed resulted in values which were in good agreement with the fermentative function of this enzyme. The alcohol dehydrogenase catalyzed the NAD (P)-dependent dismutation of acetaldehyde to acetate and ethanol. This reaction was studied in detail, and its possible involvement in acetate formation is discussed. Among various compounds tested for affecting enzyme activity only NAD, NADP, AMP, ADP, acetate and 2-mercaptoethanol exhibited significant effects.

Bacterial 2,3-butanediol dehydrogenases

Enterobacter aerogenes, Aeromonas hydrophila, Serratia marcescens and Staphylococcus aureus possessing L(+)-butanediol dehydrogenase produced mainly meso-butanediol and small amounts of optically active butanediol; Acetobacter suboxydans, Bacillus polymyxa and Erwinia carotovora containing D(-)-butanediol dehydrogenase produced more optically active butanediol than meso-butanediol. Resting and growing cells of these organisms oxidezed only one enantiomer of racemic butanediol. The D(-)-butanediol dehydrogenase from Bacillus polymyxa was partially purified (30-fold) with a specific activity of 24.5. Except NAD and NADH no other cofactors were required. Optimum pH-values for oxidation and reduction were pH 9 and pH 7, respectively. The optimum temperature was about 60 degrees C. The molecular weight was 100000 to 107000. The Km-values were 3.3 mM for D(-)butanediol, 6.25 mM for meso-butanediol, 0.53 mM for acetoin, 0.2 mM for NAD, 0.1 mM for NADH, 87 mM for diacetyl, 38 mM for 1,2-propanediol; 2,3-pentanedion was not a substrate for this enzyme. The L(+)butanediol dehydrogenase from Serratia marcescens was purified 57-fold (specific activity 22.3). Besides NAD or NADH no cofactors were required. The optimum value for oxidation was about pH9 and for reduction pH 4.5. The optimum temperature was 32-36 degrees C. The molecular weight was 100000 to 107000. The Km-values were 5 mM for meso-butanediol, 10 mM for racemic butanediol, 6.45 for acetoin, 1 mM for NAD, 0.25 mM for NADH, 2.08 mM for diacetyl, 16.7 mM for 2,3-pentanedion and 11.8 mM for 1,2-propanediol.

Purification and properties of a diacetyl reductase from Escherichia coli

A reduced nicotinamide adenine dinucleotide phosphate (NADPH)-dependent reductase with the ability to reduce diacetyl has been isolated from Escherichia coli and has been purified 800-fold to near homogeneity. The product of the reduction of diacetyl was shown to be acetoin. The enzyme proved to catalyze the oxidation of NADPH in the presence of both uncharged alpha- and beta-dicarbonyl compounds. Even monocarbonyl compounds showed slight activity with the enzyme. On the basis of its substrate specificity, it is suggested that the enzyme functions as a diacetyl reductase. In contrast to other diacetyl reductases, the one reported here is specific for NADPH and does not possess acetoin reductase activity. The pH optimum of this enzyme was found to be between 6 and 7. The maximal velocity for the NADPH-dependent reduction of diacetyl was determined to be 9.5 mumol per min per mg of protein and the K(m) values for diacetyl and NADPH were found to be 4.44 mM and 0.02 mM, respectively. The molecular weight was estimated by gel filtration on Sephadex G-100 to be approximately 10,000.