Enzymes oxygen

Based on reactions they catalyze, enzymes can be broadly classified into six major categories (Table 1.1) [1], It was estimated that about 60% of biotransformations currently rely on the use of hydrolases, followed by 20% of oxidoreductases [2]. On the other hand, some of the C—C bond-forming and oxygenation enzymes catalyze reactions with very high reaction efficiency and very low waste generation, underlining the potential of emerging enzymes. 

In vitro studies on the S oxygenating enzyme involved in cyanatryn metabolism... 

This sequence is apparently applicable to the cytochrome oxidase-oxygen enzyme-substrate compound, where the apparent dissociation constant is relatively large (0.5 mAf at —120°) 150). At higher temperatures, however, compounds are formed in which the reversibility can no longer be identified in spite of a number of efforts to do so 152, 153). 

Besides the oxygenating enzyme, NADPH and oxygen, the procedure utilizes a regeneration system for reduced nicotinamide cofactor that is based on glucose-6-phosphate and glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides394. 

Since the isolation of the oxygenating enzyme and recycling of the cofactor is still difficult for large-scale preparations, the use of whole microorganisms would seem to be advantageous. Whole cells of Acinetobacter are well suited for enantioselective Baeyer-Villiger oxidation of cyclic ketones when a lactone hydrolase inhibitor is used or a hydrolase deficient mutant is... 

FIGURE 15.4 The structures of riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). Even in organisms that rely on the nicotinamide coenzymes (NADH and NADPH) for many of their oxidation-reduction cycles, the flavin coenzymes fill essential roles. Flavins are stronger oxidizing agents than NAD and NADP. They can be reduced by both one-electron and two-electron pathways and can be reoxidized easily by molecular oxygen. Enzymes that use flavins to carry out their reactions—flavoenzymes—are involved in many kinds of oxidation-reduction reactions. 

Chilling Stress and Active-Oxygen Enzymes in Zea mays and Zea diploperennis 683... 

Phenolic components can be selectively oxidized by polyphenol oxidase - one of the few available isolated oxygenating enzymes - to give o-hydroxylated products (catechols) in high yields [1131]. Unfortunately the reaction does not stop at this point but proceeds further to form unstable o-quinones, which are prone to polymerization, particularly in water (Scheme 2.153). 

Examples of this group of enzymes are the amino acid oxygenases (C 2.6.3). There is great variability in the way hydrogen that is cleaved from the co-substrates is transferred to the oxygenating enzyme. In the simplest cases it is... 

More complicated are enzymes which dehydrogenate the cosubstrate by a separate protein which itself interacts with the oxygenating enzyme. An example of this type is phenylalanine 4-monooxygenase (Fig. 17, see also D 22). 

Hansen BG, Kliebenstein DJ, Halkier BA (2007) Identification of a flavin-monooxygenase as the S-oxygenating enzyme in aliphatic glucosinolate biosynthesis in Arabidopsis. Plant J 50 902-910. 

Enzymes are present in all living plant and animal material. They are usually classified into two major categories (1) those which have a basic reaction which involves the addition of water and the breakdown of larger compounds to smaller, called hydrolytic enzymes and (2) those which cause a breakdown of a molecule without the addition of water or oxygen. Enzymes are activated by normal physiological processes, such as the destruction of the cell by such processes as grinding or crushing. Enzymes can be inactivated by heat... 

In the case of IDO, on the other hand, a relatively stable binary complex with O2, i.e., the oxygenated enzyme, can be formed even in the absence of substrate [192, 201]. The enzyme-oxygen species, (E O2 Fe -02 or Fe -02"), exhibits absorption maxima at 415, 542, and 576 nm as shown in Fig. 23 [203]. The binary species is formed by the native ferric enzyme with superoxide anion [201] or by the binding of dioxygen to the ferrous enzyme [166, 178, 201, 202, 204]. Sono stabilized the IDO-O2 binary complex at -30 oc [203] and observed the spectral change by addition of tryptophan to the binary complex. 

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