Formation of 2,3-pentanediol from 2,3-pentanedione and acetylethylcarbinol by diacetyl(acetoin)reductase from Aerobacter aerogenes. A possible new pathway

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.

Kinetics of the diacetyl and 2,3-pentanedione reduction by diacetyl reductase (alpha-diketone reductase (NAD)) from Staphylococcus aureus

The kinetic mechanism of diacetyl and 2,3-pentanedione reduction by diacetyl reductase from Staphylococcus aureus was investigated. The shape of the primary double reciprocal plots, the product inhibition pattern, and the features of the inhibition by a substrate analogue (acetone) show that diacetyl is reduced via an Ordered Bi-Bi mechanism, and 2,3-pentanedione by an Ordered Bi-Bi or Theorell-Chance mechanism. NADH is the leading substrate in both reactions. Affinity constants for the coenzyme and the substrates and inhibition constants for NAD, acetoin, and acetone were also calculated. This enzyme has a high affinity for NADH; Km (31-50 microM) and Ks (20-27 microM) for this compound are around one-tenth of the NADH intracellular concentration. Therefore, it must operate in vivo saturated with the coenzyme. This condition is not adequate to play the role, formerly proposed for diacetyl reductases, of regulating the equilibrium between oxidized and reduced forms of pyridine-nucleotides.

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.

Further purification and characterization of diacetyl reducing enzymes from beef liver

Two diacetyl reducing enzymes have been isolated from beef liver. One of them, a monomer of mol. wt 28-30,000 dalton and pI 6.2, corresponds to the low molecular weight diacetyl reductase formerly accounted for using preparations of this organ; it has been now identified as an L-glycol dehydrogenase. The other one, an oligomer of 78,000 dalton and pI 7.0, which matches the high molecular weight diacetyl reductase, is, in the authors' opinion, a new enzyme for which the systematic name L(+)-alpha-hydroxycarbonyl: NAD(P) oxidoreductase (EC 1.1.1...) and common name alpha-dicarbonyl reductase are proposed.

Further purification and characterization of diacetyl reductase from pigeon liver

Electrophoretically pure preparation of an enzyme from pigeon liver which is classified in the I.U.B. Enzyme List as a specific diacetyl reductase (Acetoin: NAD oxidoreductase, EC 1.1.1.5) have been obtained. This enzyme has been characterized as an alpha-dicarbonyl reductase (L(+)-alpha-hydroxicarbonyl: NAD(P) oxidoreductase, EC 1.1.1...) similar to the one recently discovered from beef liver by the authors' group. Although differences in mol wt among these two reductases had been reported, both of them are oligomers of 25,000-26,000 dalton subunits.

Kinetics of alpha-dicarbonyls reduction by L-glycol dehydrogenase from hen muscle

Michaelis constants of L-glycol dehydrogenase from hen muscle (isozyme of pI 7.2) for the alpha-dicarbonyls tested (glyoxal, 2,3-pentanedione, methylglyoxal, and diacetyl) range from 35 microM for pentanedione to 0.41 mM for glyoxal. The enzyme shows a high affinity for NADPH, Km (2.2-3.1 microM), and Ks (1.2-1.9 microM) being so much lower than its tissue concentration that L-glycol dehydrogenase has to operate in vivo saturated with the coenzyme; this condition is very unfavorable to play a role in regulating the equilibrium oxidized/reduced forms of the pyridine nucleotides, as it has been proposed for some similar enzymes. Convergence of the double reciprocal plots and the pattern of inhibition by products and by acetone, a substrate analog, demonstrate that glyoxal reduction--and most likely that of diacetyl--proceeds via an ordered Bi-Bi mechanism in which NADPH is fixed before the addition of the carbonyl; the reduction of methylglyoxal and 2,3-pentanedione could follow the same model, but our experimental results are also consistent with that of Theorell-Chance.

Purification and some properties of L-glycol dehydrogenase from hen's muscle

1. An enzyme which catalyzes the NAD(P)H-linked reversible reduction of uncharged vicinal dicarbonyls and alpha-hydroxycarbonyls to L-(+)-glycols has been purified from hen's muscle. This enzyme has not been previously described. 2. According to the rules of the I.U.P.A.C.-I.U.B. Enzymes Commission, the systematic name of L-(+)-glycol:NAD(P) oxidoreductase and the trivial name of L-glycol dehydrogenase are proposed for the enzyme. 3. Three forms of this enzyme differing in pI have been isolated; two forms, which together represent about 90% of total recovered activity, and electrophoretically pure. 4. Molecular weight, pH profiles and affinity for substrates are also described.

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.