Enzymes bacterial fermentation

Redox reaetions and hydrolysis are the predominant metabolie eonversions triggered by the intestinal microflora. The main reductive enzymes produeed by the intestinal mieroflora are nitroreductase, deaminase, urea dehydroxylase, and azoreduetase the hydrolytic enzymes are P-glucoronidase, P-xylosidase, P-galaetosidase, and a-L-arabinosidase. Studies conducted by Macfarlane and co-workers have shown that proteolysis ean also happen in the colon [31]. More recent findings by this group indieate that bacterial fermentation of proteins in humans could account for 17% of... 

Frequently, hydrogen gas is also a fermentation end product in some bacterial species, protons can be used as electron acceptors by enzymes known as hydrogenases, which catalyze reactions that essentially reduce protons to hydrogen gas NADH + H+ —> H2 + NAD+. Hydrogen gas is therefore a product only of particular bacterial fermentative processes and not of human metabolism. 

Release of enzymes is not considered a problem because detergent enzymes occur naturally in the environment. In fact Bacillus species, common hosts for the production of enzymes, are found in the soil and are part of the microbial population used in com-posting.f Nevertheless, the bacterial fermentations carried out in enzyme plants are carefully contained, and no live organisms should be detectable in the final enzyme product. As an additional safety measure, engineered bacterial strains are designed so that they cannot compete effectively with natural strains in the environment. 

Song H, Lee SY (2006) Production of succinic add by bacterial fermentation. Enzyme Microb Technol 39 352-361... 

PHAs are commonly produced by bacterial fermentation during which a carbon substrate is converted into hydroxyl-CoA thioesters. These monomers are then polymerised into PHAs by the PHA-synthase enzyme, which is present in the host organism. The molecular weight of the PHAs varies from 2 x 10 —3 x 10 Da based on the type of the organism, media composition and the growth parameters used for its production (Byrom, 1987 Lee, 1996). 

The basic ingredient of PLA is lactic acid, which is yielded from bacterial fermentation or from a petrochemical source. Lactic acid is a naturally occurring substance with the standard chemical name 2-hydroxy propionic acid. It is the simplest hydroxyl acid with an asymmetric carbon atom, and has optically active L(+) and D(—) isomers. Both L and D isomers are produced in bacterial systems, with the L isomer more commonly found. Meanwhile, mammalian systems produce only the L isomer, which is easily assimilated by enzyme protease K. Figure 4.2 shows the chemical structure of the L- and D-lactic acids. 

There are a number of other polysaccharides in foods. Collectively they are known as non-starch polysaccharides, the major components of dietary fibre (section 7.3.3.2). Non-starch polysaccharides are not digested by human enzymes, although all can be fermented to some extent by intestinal bacteria, and the products of bacterial fermentation may be absorbed and metabolized as metabolic fuels. The major nonstarch polysaccharides (shown in Figure 4.8) are ... 

Deficiency of the enzyme lactase is common. Indeed, it is only in people of north European origin that lactase persists after childhood. In most other people, and in a number of Europeans, lactase is gradually lost through adolescence — alactasia (see Problem 4.2). In the absence of lactase, lactose cannot be absorbed. It remains in the intestinal lumen, where it is a substrate for bacterial fermentation to lactate (section... 

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