Morphinone reductase

Basran J, RJ Harris, MJ Sutcliffe, NS Scrutton (2003) H-tuneling in the multiple H-transfers of the catalytic cycle of morphinone reductase and in the reductive half-reaction of the homologous pentaerythritol tetranitrate reductase. J Biol Chem 278 43973-43982. 

French CE, NC Bruce (1994) Purification and characterization of morphinone reductase from Pseudomonas putida MIO. Biochem J 301 97-103. 

The report of Basran et al. (entry 5 of Table 2) contains two studies involving hydride transfer with nicotinamide cofactors. In morphinone-reductase catalyzed reduction by NADH of the flavin cofactor FMN (schematic mechanism in Fig. 5), the primary isotope effects are modest (around 4 for H/D), but exhibit a small value of Ajj/Aq (0.13) and an exalted isotopic difference in energies of activation (8.2kJ/mol) that alone would have generated an isotope effect around 30. The enthalpies of activation are in the range of 35-45 kJ/mol. This is behavior typical of Bell tunneling as discussed above. It can also be reproduced by more complex models, as will be discussed in later parts of this review. 

HYDRIDE-TRANSFER REACTIONS INVOLVING OTHER COFACTORS Morphinone reductase... 

H-Tuiweling in Morphinone Reductase and Pentaerythritol Tetranitrate Reductase 1347... 

Figure 13.2. Proposed scheme for the oxidative half-reaction of morphinone reductase. The identity of the proton donor in the oxidative half-reaction is not known.

The Old Yellow Enzyme (OYE) family of flavoproteins consist of a large group of flavin mononucleotide (FMN)-containing NAD(P)H-dependent oxidases. We will describe our work on two of these enzymes morphinone reductase... 

Mueller, N.J., Stueckler, C., Hauer, B., Baudendistel, N., Housden, H., Bruce, N. C., and Faber, K. (2010) The substrate spectra of pentaerythritol tetranitrate reductase, morphinone reductase, N-ethylmaleimide reductase and estrogen-binding protein in the asymmetric bioreduction of activated alkenes. Adv. Synth. Catal., 352, 387-394. 

Craig, D.H., Moody, P.C.E., Bmce, N.C., and Scmtton, N.S. (1998) Reductive and oxidative half-reactions of morphinone reductase from Pseudomonas putida MIO a kinetic and thermodynamic analysis. Biochemistry, 37, 7598-7607. 

Messiha, H.L., Bruce, N.C., SatteDe, B.M., Sutcliffe, M.J., Munro, A.W., and Scmtton, N.S. (2005) Role of active site residues and solvent in proton transfer and the modulation of flavin reduction potential in bacterial morphinone reductase. J. Biol. Chem., 280, 27103-27110. 

The origin of the proton abstracted by the formed carbanion was also determined by site-specific mutagenesis. Several studies showed that exchanges of a strongly conserved tyrosine residue to phenylalanine or alanine leads to an overall reduced activity [8-10]. In contrast to OYEl [8], the studies with the OYEs designated as morphinone reductase (MR) and pentaerythritol tetranitrate (PETN) suggest that solvent water is the source of the proton required for reduction [9,10]. 

One of the first examples of concurrent oxidation and reduction reactions in a three-enzyme system was reported in 1996 for the biotransformation of morphine to hydromorphone (Scheme 11.2) [6]. Specifically, the NADPH-dependent morphine-6-dehydrogenase (MDH) was coupled to the NADH-dependent morphinone reductase (MR) through the action of a cofactor aspecific (accepting both NADH and NADPH) glutamate dehydrogenase. The latter cofactor regeneration reaction not only allows the use of catalytic amounts of the cofactor but also avoids the accumulation of the reduced cofactor (NADPH) produced by morphine dehydrogenase and the consequent further reduction of hydromorphone to... 

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