Bacterial azoreductase enzymes

Bacterial azoreductase enzymes in the colon cleave the azo bond between 5-ASA and sulfapyridine, releasing the 5-ASA component. 

Alternatively, the enzyme in the gut can be utilized to control the release of the active drug in the gut. For example, sulfasalazine, which is employed in the treatment of ulcerative colitis, is a combination of sul-fapyridine and 5-aminosalicylate chemically linked via an azo bond. It remains absorbed and intact throughout the GI tract until it reaches the large intestine, where bacterial azoreductase enzymes degrade the azo bond and release sulfapyridine and 5-aminosalicylate to act locally on the lesions. 

Based on the previous publications, azo dye can be reduced by azoreductase-catalyzed reduction under anaerobic conditions. But still there is a speculation whether bacterial flavin reductases are responsible for the azo reductase activity observed with bacterial cell extracts. In a published report, it is reported that flavin reductases are indeed able to act as azo reductases [24]. Bacteria produce extracellular oxidative enzymes, which are relatively nonspecific enzymes catalyzing the oxidation of a variety of dyes. It was reported that so many diverse groups of bacteria play a role in decolorization. It has been also reported that mixed microbial community could reduce various azo dyes, and members of the y-proteabacteria and sulfate reducing bacteria (SRB) were found to be prominent members of mixed bacterial population by using molecular methods to determine the microbial population dynamics [1],... 

Redox reactions and hydrolysis are the predominant metabolic conversions triggered by the intestinal microflora. The primary reductive enzymes produced by the intestinal microflora are nitroreductase, deaminase, urea dehydroxylase, and azoreductase. The hydrolytic enzymes are p-glucuronidase, p-xylosidase, p-galactosidase, and ot-L-arabinosidase. Studies conducted by Macfarlane and coworkers have shown that proteolysis can also occur in the colon. More recent findings by the group indicate that bacterial fermentation of proteins in humans could account for 17% of the short-chain fatty acids in the cecum and for 38 /o in the sigmoid and the rectum. ... 

In addition to the oxidative systems, liver microsomes also contain enzyme systems that catalyze the reduction of azo and nitro compounds to primary amines. A number of azo compounds, such as Prontosil ahd sulfasalazine (Fig. 10.16), are converted to aromatic primary amines by azoreductase, an NADPFI-dependent enzyme system in the liver microsomes. Evidence exists for the participation of CYP450 in some reductions. Nitro compounds (e.g., chloramphenicol and nitrobenzene) are reduced to aromatic primary amines by a nitroreductase, presumably through hitrosamine and hydroxylamine intermediates. These reductases are not solely responsible for the reduction of azo ahd hitro compouhds reductioh by the bacterial flora ih the anaerobic environment of the intestine also may occur. 

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