Kinetics and thermodynamics of diacetyl reduction with NADPH by alpha-dicarbonyl reductase from pigeon liver

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.

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.