Microorganism oxygenases

Assuming the NP biotransformation is limited by reactions with such an oxygenase in groundwater microorganisms, what kbl0 would you estimate for NP ... 

The genes coding for oxygenases have been studied in a wide variety of hydrocarbon-degrading microorganisms. They are usually organized in inducible operons and can be located either on the chromosomes or on plasmids. 

Enzymes that directly incorporate molecular oxygen into organic substrates play a crucial role in many fundamental biological processes such as degradation of natural products in the biosphere, biosynthesis and metabolism of amino acids, hormones, drugs, etc. A wide variety of enzymic oxygenases has been identified and isolated from microorganisms, plants and animals. A detailed description of these enzymes is beyond the scope of this chapter, but several books and review articles are available.1,58-62... 

It is well-known that plants do not synthesize vitamin A. Also, animals can only synthesize vitamin A from p-carotene or carotenoids in which one-half of the molecule is like p-carotene. In nature, the vitamin A precursor comes either from plants or microorganisms. The most common sources of vitamin A in citrus are a- and p-carotenes and p-cryptoxanthin. In addition to the above name carotenoids, p-apo-8 -carotenal in citrus peel could be a source of provitamin A. However, the peel is not usually consumed. Provitamin A compounds are cleaved to form vitamin A aldehyde in the intestine by p-carotene 15,15 -oxygenase (Figure 4) (54). Aldehyde reductase reduces the aldehyde to the all trans-vitamin A. p-Carotene is cleaved between the 15,15 carbon... 

The hydrolytic and reductive capabilities of microorganisms, especially fungi, are extremely useful in evaluating the metabolic fate of drugs [18-21]. For instance, many pathways of oxidative reactions parallel the same ones in mammals. In addition, fungi have been shown to possess mono-oxygenase enzyme systems... 

Elsaied H. and Nayunama T. (2001) Phylogenetic diversity of Ribulose-1,5-Birphosphate Carboxylase/Oxygenase large-subunit genes from deep sea microorganisms. Appl. Environ. Microbiol. 67, 1751-1765. 

The Calvin cycle or reductive pentose phosphate cycle occurs in all green plants and many microorganisms. Carboxylation is catalyzed by ribulose-bis-phosphate carboxylase-oxygenase (Rubisco). Rubisco also functions as an oxygenase during photorespiration, but its affinity for O2 is 20-80 times lower than for CO2. As with most enzymes, Rubisco has a preference for lighter stable isotopes and CO2 fixation results in the depletion of C (5 C) ranging from —10%o to —2Q%c. 

In comparison to all other heterotrophs, the microorganisms oxidizing methane and other Cj compounds such as methanol, have a unique metabolic pathway which involves oxygenase enzymes and thus requires O. Only aerobic methane-oxidizing bacteria have been isolated and studied in laboratory culture, yet methane oxidation in marine sediments is known to take place mostly anaerobically at the transition to the sulfate zone. Microbial consortia that oxidize methane with sulfate have in particular been studied at methane seeps on the sea floor and the communities can now also be grown in the laboratory (Boetius et al. 2000 Orphan et al. 2001 Nauhaus et al. 2002) Anaerobic methane oxidation is catalyzed by archaea that use a key enzyme related to the coenzyme-M reductase of methanogens, to attack the methane molecule (Kruger et al. 2003 see Sect. 5.1). The best studied of these ANME (ANaerobic MEthane... 

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