Enzyme catalyzed reaction from microorganism

Microbial biofuel cells were the earliest biofuel cell technology to be developed, as an alternative to conventional fuel cell technology. The concept and performance of several microbial biofuel cells have been summarized in recent review chapters." The most fuel-efficient way of utilizing complex fuels, such as carbohydrates, is by using microbial biofuel cells where the oxidation process involves a cascade of enzyme-catalyzed reactions. The two classical methods of operating the microbial fuel cells are (1) utilization of the electroactive metabolite produced by the fermentation of the fuel substrate " and (2) use of redox mediators to shuttle electrons from the metabolic pathway of the microorganism to the electrodes. ... 

Animals and plants cannot synthesize vitamin B12. In fact, only a few microorganisms can synthesize it. Humans must obtain all their vitamin B12 from their diet, particularly from meat. Because vitamin B12 is needed in only very small amounts, deficiencies caused by consumption of insufficient amounts of the vitamin are rare, but have been found in vegetarians who eat no animal products. Deficiencies are most commonly caused by an inability to absorb the vitamin in the intestine. The deficiency causes pernicious anemia. The following are examples of enzyme-catalyzed reactions that require coenzyme B12 ... 

The production of thermostable enzymes, catalyzing reactions at high temperatures, is one of the most attractive features of thermophilic microorganisms. In order to select producers of thermostable hydrolases, different aerobic thermophilic bacterial strains were Isolated from water, soil and organic material samples collected from Bulgarian hot springs environment. Some of the properties of the Isolated strains were a subject of our previous work [1]. The aim of the present paper was to characterize and identify the strain producing thermostable pullulanase as well as to establish the optimum conditions for enzyme production and to study some of the enzyme s properties. 

Contrary to common chemical reactions, enzyme-catalyzed reactions as well as growth of microorganisms show a so-called temperature optimum, which is a temperature-dependent maximum resulting from the overlapping of two counter effects with significantly different activation energies (cf. 2.5.4.2) ... 

Enzyme-catalyzed reactions in food processing have been used unintentionally since ancient times. The enzymes are either an integral part of the food or are obtained from microorganisms. Addition of enriched or purified enzyme preparations of animal, plant or, especially, microbial origin is a recent practice. Most of these enzymes come from microorganisms, which have been genetically modified in view of their economic production. Such intentionally used... 

There are two distinct groups of aldolases. Type I aldolases, found in higher plants and animals, require no metal cofactor and catalyze aldol addition via Schiff base formation between the lysiae S-amino group of the enzyme and a carbonyl group of the substrate. Class II aldolases are found primarily ia microorganisms and utilize a divalent ziac to activate the electrophilic component of the reaction. The most studied aldolases are fmctose-1,6-diphosphate (FDP) enzymes from rabbit muscle, rabbit muscle adolase (RAMA), and a Zn " -containing aldolase from E. coli. In vivo these enzymes catalyze the reversible reaction of D-glyceraldehyde-3-phosphate [591-57-1] (G-3-P) and dihydroxyacetone phosphate [57-04-5] (DHAP). 

Capillary gas chromatographic determination of optical purities, investigation of the conversion of potential precursors, and characterization of enzymes catalyzing these reactions were applied to study the biogenesis of chiral volatiles in plants and microorganisms. Major pineapple constituents are present as mixtures of enantiomers. Reductions, chain elongation, and hydration were shown to be involved in the biosynthesis of hydroxy acid esters and lactones. Reduction of methyl ketones and subsequent enantioselective metabolization by Penicillium citrinum were studied as model reactions to rationalize ratios of enantiomers of secondary alcohols in natural systems. The formation of optically pure enantiomers of aliphatic secondary alcohols and hydroxy acid esters using oxidoreductases from baker s yeast was demonstrated. 

Whereas plants and certain microorganisms can generate all required coenzymes from CO2 or simple organic precursors, animals must obtain precursors (designated as vitamins) for a major fraction of their coenzymes from nutritional sources. Still, most vitamins must be converted into the actual coenzymes by reactions catalyzed by animal enzymes. The structures and biosynthetic pathways of some coenzymes are characterized by extraordinary complexity. Enzymes for coenzyme biosynthesis have frequently low catalytic rates, and some of them catalyze reactions with highly unusual mechanisms. 

More than 10,000 enzymes occur in nature. Of these, approx. 3,000 are characterized. Approx. 800 are commercially available, but only approx. 20 in industrial amounts (predominantly hydrolases and oxidoreductases). They are isolated from microorganisms, plants, or animals. Lipases (which belong to the class of hydrolases) and oxidoreductases catalyze, for example, the reactions depicted in Fig. 3.6. Note that all reactions are reversible. Examples of flavouring substances that are produced with lipases and oxidoreductases are shown in Tab. 3.12. 

---