A-Keto glutarate

Scheme 10.31 Reaction cycle of KG-dependent (KG = a-keto-glutarate) enzymes. Metal ligands from protein side chains and water are omitted for clarity. One of the oxygens of O2 is incorporated into succinate. The other oxygen is either incorporated into the product or reduced to water depending on the nature of the reaction.

These mechanisms for the synthesis of glycine present a partial barrier to the movement of FA carbons into this molecule, the most abimdant AA in collagen. On the other hand, proline is synthesized from a-keto glutarate which can be freely derived from either carbohydrates or FAs thus the synthesis of pro line does not present a barrier to entry ofFA-derived carbons into collagen. 

Fukumori F, RP Hausinger (1993b) Purification and characterization of 2,4-dichlorophenoxyacetate/a-keto-glutarate dioxygenase. J Biol Chem 268 24311-24317. 

Among the mononuclear non-haem iron enzymes catalysing hydroxylation reactions (Table 2.3) we can distinguish between intramolecular dioxygenases and external mononoxygenases. The former can be divided into those which are pterin-dependent and those which use a-ketoacids such as a-keto glutarate as obligatory... 

Answer E. Most important TPP-dependent enzymes include pyruvate dehydrogenase, a-keto-glutarate dehydrogenase, and transketolase. Transketolase is in the HMP shunt and is not strictly essential for glucose oxidation. 

Alanine, aspartate, and glutamate are synthesized by transfer of an amino group to the a-keto acids pyruvate, oxaloacetate, and a-keto-glutarate, respectively. These transamination reactions (Figure 20.12, and see p. 248) are the most direct of the biosynthetic pathways. Glutamate is unusual in that it can also be synthesized by the reverse of oxidative deamination, catalyzed by glutamate dehydrogenase (see p. 249). 

A. Structure of thiamine and its cofactor form, thiamine pyrophosphate. B. Structure of intermediate formed in the reaction catalyzed by pyruvate dehydrogenase. C. Structure of intermediate formed in the reaction catalyzed by a-keto-glutarate dehydrogenase. 

Bromate, chloride, bromide, nitrite, nitrate, hypophosphite (HP022 ), selenite, selenate, sulphate, phosphate, pyrophosphate, arsenate, chromate, a-hydroxybutyrate, butyrate, formate, acetate, glycolate, gluconate, valerate, a-hydroxy valerate, pyruvate, monochloroacetate, dichloroacetate, trifluoroacetate, galactonurate, gluconurate, a-keto-glutarate, oxalate, fumarate, phthalate, oxalacetate, citrate, isocitrate, cis aconitate, trans aconitate, succinate, maleate, malonate, quinate, tartrate, hexane sulphonate, octane sulphonate, octane sulphate, decane sulphonate, dodecane sulphonate and dodecane sulphate... 

Amino acids get used up (making proteins, for example) so, to keep life going, ammonia must be brought in from somewhere. The key amino acid in this link is glutamic acid. A true reductive animation using NADPH and ammonia builds glutamic acid from a-keto-glutaric acid. 

Aminotransferases catalyze the transfer of an a-amino group from an a-amino acid to an a-ketoacid. These enzymes, also called transaminases, generally funnel a-amino groups from a variety of amino acids to a-keto-glutarate for conversion into NH4 +. 

Most amino acids are deaminated by transamination reaction catalysed by aminotransferases or transaminases. The a-amino group present in an amino acid is transferred to an a-keto acid to yield a new amino acid and the a-keto acid of the original amino acid. The predominant amino group acceptor is a-keto glutarate. 

There exists clear evidences that OATl plays a major role in PAH and other organic anion secretion. It is localized in the basolateral membrane of proximal tubule, it has the transport characteristics of basolateral membrane transport, i.e. it is an organic anion/a-keto-glutarate exchanger, and transport is dependent on the presence of chloride in the extracellular medium. The recent observation that the expression of rat OATl is strongly increased at birth is compatible with the fact that the PAH secretory system develops post-natal [83]. 

Aconitase catalyzes the isomerization of citrate to isodtrate, isocitrate dehydrogenase catalyzes the oxidative decarboxylation of isocitrate to a-ketoglutarate, and a-ketoglutarate dehydrogenase catalyzes the oxidative decarboxylation of a-keto-glutarate to succinyl-CoA. Succinyl-CoA and the remaining intermediates are the 4-carbon intermediates of the Krebs cycle. Succinyl thiokinase catalyzes the release of coenzyme A from succinyl-CoA and the production of GTP. Succinate dehydro-... 

The full structures of pyridoxamine and pyridoxal are on p. 1384. The incorporation of ammor. into a-keto-glutarate and the formation of glutamic acid by NADPH reduction of the imine is -p. 1386. The transamination from glutamic acid to pyridoxamine is on p. 1385. We start fr -pyridoxamine, whose structure we abbreviate, and pyruvate. Imine formation (fiiU mechanism pp. 348-50) followed by proton removal and replacement gives a new imine whose hydrolysis (f mechanism on pp. 350-1) gives alanine and pyridoxal. The alanine is a single enantiomer beca.s enzyme-directed protonation occurs on one face of the imine. Pyridoxal is recycled transamination with glutamic acid. 

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