Dehydratases

Lyases. These enzymes cleave C-C, C-0, C-N and other bonds by elimination leaving double bonds or conversely add groups to double bonds. This group includes decarboxylases, hydratases, dehydratases and some carboxylases. 

This reaction is catalyzed by an enzyme called a dehydratase and is one step along the pathway by which plants convert glucose to certain ammo acids... 

Lead-induced anemia results from impairment of heme biosynthesis and acceleration of red blood cell destmction (10,13). Lead-induced inhibition of heme biosynthesis is caused by inhibition of S-aminolevulinic acid dehydratase and ferrochelatase which starts to occur at blood lead levels of 10 to 20 pu gjdL and 25 to 30 //g/dL, respectively (10,13). Anemia, however, is not manifested until higher levels are reached. 

L-glutamic acid C. melassecola C. melassecola Glu A, citrate dehydrogenase, ppc, aconitate dehydratase ... 

Aminolevulinic acid dehydratase 3-aminotriazole toxicity to, 1, 139 Aminopterin—see Folic acid, 4-amino-Aminopyrine as antipyretic, 1, 172 biological activity, 5, 295 Aminyl, dimethyl-ESR, 7, 19 Amiphenazole... 

ALAD (8-aminolevulinic acid dehydratase) Aldehydes (screening)... 

Pyridoxamine phosphate serves as a coenzyme of transaminases, e.g., lysyl oxidase (collagen biosynthesis), serine hydroxymethyl transferase (Cl-metabolism), S-aminolevulinate synthase (porphyrin biosynthesis), glycogen phosphoiylase (mobilization of glycogen), aspartate aminotransferase (transamination), alanine aminotransferase (transamination), kynureninase (biosynthesis of niacin), glutamate decarboxylase (biosynthesis of GABA), tyrosine decarboxylase (biosynthesis of tyramine), serine dehydratase ((3-elimination), cystathionine 3-synthase (metabolism of methionine), and cystathionine y-lyase (y-elimination). 

Towards the unification of coenzyme B12-dependent diol dehydratase stereochemical and model studies the bound radical mechanism. R. G. Finke, D. A. Schiraldi and B. J. Mayer, Coord. Chem. Rev., 1984, 54,1-22 (40). 

In industrial processes, 1,3-propanediol is used for the production of polyester fibers, polyurethanes and cydic compounds [85]. 1,3-Propanediol can be produced from glucose with the limiting step catalyzed by glycerol dehydratase. A metagenomic survey for glycerol hydratases from the environment resulted in seven positive clones, one of which displayed a level of catalytic efficiency and stability making it ideal for application in the produdion of 1,3-propanediol from glucose. 

Aminolaevulinate dehydratase (ALA-D) (EC 4.2.1.24) in mice and rats livers was determined after 7-fold administration of the studied compounds according to Berlin (ref. 17), as modified by Schlick et al. (ref. 18). 5-Aminolaevulinate synthase (ALA-S) (EC 2.3.1.37) was also assayed in the liver according to Sassa and Granick (ref. 19). 

Chattaraj PK, Parr RG (1993) Density Functional Theory of Chemical Hardness. 80 11-26 Cheh AM, Neilands JP (1976) The j -Aminoevulinate Dehydratases Molecular and Environmental Properties. 29 123-169 Chimiak A, Neilands JB (1984) Lysine Analogues of Siderophores. 58 89-96 Christensen JJ, see Izatt RM (1973) 16 161-189... 

Lastly, it is worth mentioning the case of the dihydroxy-acid dehydratase from spinach, in which the reduced form of a [2Fe-2S] center was found to exhibit a heterogeneous EPR spectrum of the gav === 1-91 type, indicating the presence of noncysteinyl ligands at the reducible site. This signal was converted into a gav 1-96 type spectrum upon addition of the substrate, which suggests that this center may be involved in the catalytic cycle 264). 

Figure 32-5. Biosynthesis of porphobiiinogen. ALA synthase occurs in the mitochondria, whereas ALA dehydratase is present in the cytosol.

ALA dehydratase deficiency (hepatic) (MIM 125270) Acute intermittent porphyria (hepatic) (MIM 176000) Congenital erythropoietic (erythropoietic) (MIM 263700)... 

High levels of lead can affect heme metabohsm by combining with SH groups in enzymes such as fer-rochelatase and ALA dehydratase. This affects porphyrin metabolism. Elevated levels of protoporphyrin are found in red blood cells, and elevated levels of ALA and of coproporphyrin are found in urine. 

Various minor hematological effects have been noted in animals. Rats exposed to 50-800 ppm of trichloroethylene continuously for 48 or 240 hours showed time- and dose-related depression of delta-aminolevulinate dehydratase activity in liver, bone marrow, and erythrocytes (Fujita et al. 1984 Koizumi et al. 1984). Related effects included increased delta-aminolevulinic acid (ALA) synthetase activity, reduced heme saturation of tryptophan pyrrolase and reduced cytochrome P-450 levels in the liver and increased urinary excretion of... 

Fujita H, Koizumi A, Yamamoto M, et al. 1984. Inhibition of delta-aminolevulinate dehydratase in trichloroethylene-exposed rats, and the effects on heme regulation. Biochem Biophys Acta 800 1-10. 

Most of the subsequent steps of tetrapyrrole synthesis are identical in plants, animals, and bacteria. The pathway includes synthesis of the monopyrrole porphobilinogen from two molecules of ALA by the action of ALA dehydratase with the elimination of two molecules of water, followed by the assembling of a linear tetrapyrrole hydroxymethylbilane from fonr molecnles of porphobilinogen, ring closure and two modification reactions of side chains. This produces the first tetrapyrrole macrocycle, uroporphyrinogen HI. Therefore, eight molecules of ALA are necessary to form one tetrapyrrole. 

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