Oxygenase

Hydroxylation and epoxidation reactions performed by monooxygenases are of particular interest, the cytochrome P450 monooxygenases representing a superfamily that catalyzes such reactions. 

Excellent examples of protein engineering work on dioxygenases are given in Section 10.8, changing the regio- and stereoselectivity on Rieske non-heme iron 

Change of Enantioselectivity with Site-Specific Mutagenesis 

Lipase AH (Amano, Najoya, Japan) from Pseudomonas sp. and Lipase PS (Amano, Najoya, Japan) from Pseudomonas cepacia in particular have been demonstrated to be useful for production, especially for enantiomerically pure secondary alcohols in organic media (Hirose, 1995) (Chapter 12, Section 12.6). Despite almost identical amino acid sequences in the two enzymes (their proteins differ only in 16 amino acid residues), these two lipases exhibit opposite enantioselectivity. As no crystal structure of these enzymes was available, all experiments were based on knowledge of the primary sequence. 

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Other experiments with Gibberellafujikuroi the fungus that produces gibbereUin, indicate that GA production is blocked by BAS 111. Very detailed and carehil experiments conducted with enzymes in ceU-free systems strongly support this mode of action, ie, using /-kaurene oxidase and cinnamate 4-mono-oxygenase isolated from pea apices and soybean suspension cells, and avanone-2-hydtoxylase and dibydroxypterocarpane 6-hydtoxylase from soybean suspension cells (31). 

Cytochrome P-450 is frequently the oxygenase which detoxifies xenobiotics, including herbicides. Blocking the metaboHsm of a herbicide increases the activity or delays the inactivation, thus increasing the effectiveness of such herbicides as chlortoluron [15545-48-9] and bentazon [25057-89-0]... 

Anhydrotetracycline oxygenase from Streptomjces aureofaciens which cataly2es the conversion of anhydrotetracycline to dehydrotetracycline, has been isolated and characterized as a flavin-dependent oxygenase (83). It consists of two subunits of mol wt = 57, 500 based on SDS/polyacrylamide—gel electrophoresis. The cosynthetic factor 1 of Streptomjces aureofaciens involved in the reduction of 5a,lla-dehydrochlortetracycline to chlortetracycline, has been identified as 7,8-didemethyl-8-hydroxy-5-deazariboflavin. This work was aided by comparison of spectral data with that of an authentic sample obtained from the hydrolysis of coenzyme F-420 (84). 

As indicated, ribulose bisphosphate carboxylase/oxygenase catalyzes an alternative reaction in which Og replaces COg as the substrate added to RuBP (Figure 22.29a). The ribulose-l,5-bisphosphate oxygenase rezLCtion diminishes plant... 

Miziorko, H. M., and Lorimer, G. H., 1983. Ribnlose-l,5-bisphosphate car-boxylase/oxygenase. Annual Review of Biochemistry 52 507-535. An early review of die enzymological properties of rnbisco. 

Pords, A. R., Jr., 1992. Regnladon of ribnlose 1,5-bisphosphate carboxy-lase/oxygenase acdvity. Annual Review of Plant Physiology and Plant Molecular Biology 43 415—437. 

Scheme 10.6 Byproducts of cytochrome P450 oxygenase catalyzed epoxidation. Top N-alkylation of the porphyrin ring. Bottom group migration to give aldehydes. 

Nothing is known about the identity of the iron species responsible for dehydrogenation of the substrate. Iron-oxo species such as FeIV=0 or Fem-OOH are postulated as the oxidants in most heme or non-heme iron oxygenases. It has to be considered that any mechanistic model proposed must account not only for the observed stereochemistry but also for the lack of hydroxylation activity and its inability to convert the olefinic substrate. Furthermore, no HppE sequence homo-logue is to be found in protein databases. Further studies should shed more light on the mechanism with which this unique enzyme operates. 

Oxygenases - add one (monooxygenases) or both (dioxygenases) atoms of molecular oxygen to molecules, eg... 

The lower than expected yields can be explained by the nature of methane oxidation to methanol in these bacteria. This reaction, catalysed by methane mono-oxygenase, is a net consumer of reducing equivalents (NADH), which would otherwise be directed to ATP generation and biosynthesis. In simple terms the oxidation of methane to methanol consumes energy, lowering the yield. 

Samuel, D. (1962). Methodology of oxygen isotopes. In Hayaishi, O. (ed.), Oxygenases, pp. 31-86. Academic Press, New York. 

P450 Mono-oxygenase System Reactive Oxygene Species Oxidative Stress Vitamin C Vitamin E... 

Targeted Cancer Therapy P450 Mono-Oxygenase System... 

P450 Mono-Oxygenase System P450 Enzymes... 

All mammalian cells are virtually capable of producing CO with heme as the main substrate (Fig. 1) [5]. Enzymatic heme metabolism in vivo is mainly catalyzed by heme oxygenase (HO). In the presence of HO, the porphyrin ring of heme is broken and oxidized at the a-methene bridge, producing equimolar amounts of CO, ferrous iron, and biliverdin. Three isoforms of HO have been identified. Inducible HO-1 (32 kDa) is mostly recognized for its upregulation in response... 

Carbon Monoxide. Figure 1 Heme oxygenase catalyzed heme metabolism (from Pharmacol Rev 57 585-630,... 

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