Oxygen reaction with enzymes

An interesting combination of enzymatic with non-enzymatic transformation in a one-pot three-step multiple sequence was reported by Waldmann and coworkers [82]. Phenols 125 in the presence of oxygen and enzyme tyrosinase are hydroxylated to catechols 126 which are then oxidized in situ to ortho quinones 127. These intermediates subsequently undergo a Diels-Alder reaction with inverse electron demand by reaction with different dienophiles (Table 4.19) to give endo bicyclic 1,2-diketones 128 and 129 in good yields. 

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. 

Compared with Molsidomine, both SIN-1 and SIN-1A are reported to induce similar, but more rapid hypotensive action [95, 96]. SIN-1A, after undergoing oxidation in the presence of oxygen or, in vivo, possibly by redox-active enzymes such as cytochrome C [97, 98] or by reaction with ferric myoglobin formed during reperfusion injury [99], releases NO through an intermediate radical cation. 

Copper enzymes are involved in reactions with a large number of other, mostly inorganic substrates. In addition to its role in oxygen and superoxide activation described above, copper is also involved in enzymes that activate methane, nitrite and nitrous oxide. The structure of particulate methane mono-oxygenase from the methanotrophic bacteria Methylococcus capsulatus has been determined at a resolution of 2.8 A. It is a trimer with an a3P33 polypeptide arrangement. Two metal centres, modelled as mononuclear and dinuclear copper, are located in the soluble part of each P-subunit, which resembles CcOx subunit II. A third metal centre, occupied by Zn in the crystal, is located within the membrane. 

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