This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Carboxylates Degradation|
Expected Taxonomic Range: Bacteria
Citrate lyase is an anaerobic enzyme that catalyzes the cleavage of citrate to acetate and oxaloacetate [Nilekani83] (see citrate degradation). Because the citrate molecule is very stable, it has to be activated by forming a thioester bond with the enzyme before cleavage can take place.
The enzyme is a complex of three subunits (in a 6:6:6 configuration), one of them a dedicated acyl carrier protein (acp). The acp protein is synthesized in an apo form, and is converted to its fully active form in two steps - first, a holo form is generated by the covalent binding of the prosthetic group 2'-(5''-phosphoribosyl)-3'-dephospho-CoA to a serine residue. Next, the holo form is acetylated, either by EC 220.127.116.11, [citrate (pro-3S)-lyase] ligase, which uses acetate as the donor, or by EC 18.104.22.168, deacetyl-[citrate-(pro-3S)-lyase] S-acetyltransferase, that uses S-acetyl phosphopantetheine as the acetyl donor (see citrate lyase activation).
The α subunit of the citrate lyase is EC 22.214.171.124, citrate CoA-transferase, an enzyme that catalyzes the exchange of the bound acetyl group with a citrate molecule, generating a citryl-[holo citrate lyase acyl-carrier protein] and releasing an acetate molecule. The β subunit, EC 126.96.36.199, citryl-CoA lyase, catalyzes the subsequent step, cleaving the bound citryl group, releasing oxaloacetate and regenerating an acetyl-[holo citrate lyase acyl-carrier protein]. Since the active form is regenrated, the enzyme can continuously catalyze the cleavage reaction.
Genes complementary to the bacterial citrate lyase β subunit have been identified in the mouse and human genomes [Morikawa01a]. The physiological role of these genes in eukaryotes is not known yet.
Morikawa01a: Morikawa J, Nishimura Y, Uchida A, Tanaka T (2001). "Molecular cloning of novel mouse and human putative citrate lyase beta-subunit." Biochem Biophys Res Commun 289(5);1282-6. PMID: 11741334
Singh73: Singh M, Bottger B, Stewart C, Brooks GC, Srere PA (1973). "S-acetyl phosphopantetheine: deacetyl citrate lyase S-acetyl transferase from Klebsiella aerogenes." Biochem Biophys Res Commun 53(1);1-9. PMID: 4741546
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