Dehydratases citrate dehydratase

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

Fig. 1.2 Intermediates of the citric acid cycle showing the relationship between glutamate and aspartate. Pyruvate dehydrogenase complex (1) citrate synthase (2) aconitase (3) isocitrate dehydrogenase (4) a-ketoglutarate dehydrogenase (5) succinyl-CoA synthetase (6) fumarate (7) fumarase dehydratase (8) malate dehydrogenase (9) and aspartate aminotransferase (10)...

Aconitase is the trivial name for citrate dehydratase cw-aconitate hydratase (EC 4.2.1.3). It catalyzes the reversible isomerization reaction of citrate into isocitrate via the intermediate cA-aconitate (Figure 2). It is a water-soluble, monomeric protein. In eukaryotic cells aconitase is located in the mitochondrial matrix. In prokaryotes the enzyme occurs in the cytoplasma. The pig heart enzyme consists of 754 amino-acid residues, providing a molecular mass of 83 kDa [27], Aconitase from other sources has similar size. The porcine protein is synthesized with a mitochondrial targeting sequence. The mature, functional protein can be (over)expressed in Escherichia coli [28],... 

The substrates of serine dehydratase [45,46] and dihydroxyacid dehydratase [47] differ from citrate in more than just R. The different substrates are compared in Figure 4. They all have in common the central HO —C—CH COO- fragment, indicating that all enzymes should have the following features ... 

In this reaction, the tertiary alcoholic group of citrate is converted to a secondary alcoholic group that is more readily oxidized. The isomerization catalyzed by aconi-tate dehydratase (or aconitase) occurs by removal and addition of water with the formation of an intermediate, c -aconitate ... 

A powerful competitive inhibitor (highly toxic) of aconitate dehydratase is fluorocitrate, an analogue of citrate ... 

Other C-0 lyase enzymes include aconitate hydratase or aconitase (E. C. 4.2.1.3), an enzyme that catalyzes two tricarboxylic acid cycle steps from isocitric acid to citrate (14)1141 or vice versa, via the intermediate cis-aconitate (13). Citrate dehydratase (E. C. 4.2.1.4) is only capable of converting citrate to cis-aconitate and does not act on isocitrate (15) 115l... 

Abbreviations FASN, fatty acid synthase ACC, acetyl-CoA-carboxylase ACL, ATP-citrate lyase NADPH, nicotinamide adenine dinucleotide phosphate MAT, malonyl acetyl transferases KS, ketoacyl synthase KR, p-ketoacyl reductase DH, p-hydroxyacyl dehydratase ER, enoyl reductase TE, thioesterase ACP, acyl carrier protein VLCFA, very long chain fatty acids ELOVL, elongation of very long chain fatty acids SCDl, stearoyl-CoA desaturase-1 AMPK, AMP-activated kinase ME, malic enzyme FASKOL, liver-specific deletion of FAS PPARa, Peroxisome Proliferator-Activating Receptor alpha HMG-CoA, 3-hydroxy-3-methyl-glutaryl-CoA SREBP, sterol response element binding protein SIP, site-one protease S2P, site-two... 

This broad class of enzymes also includes dehydratases and many synthases. Dehydratases remove the elements of water from two adjacent carbon-carbon bonds to form a double bond. Certain enzymes in this group, such as certain group transferases, are commonly called synthases when the physiologically important direction of the reaction favors the formation of a carbon-carbon bond (e.g., citrate synthase). 

Note Another family of serine dehydratases does not use pyridoxal phosphate, but rather an iron-sulfur cluster as the cofactor. These enzymes may use a mechanism similar to the dehydration of citrate catalyzed by aconitase. See Trends Biochem. Sci. 18[ 19931 297-300.)... 

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