 This pathway has been shown to be present in several yeast species, as well as protists and higher fungi.It has also been reported that an alternative variant of the AAA route has been found in "Thermus thermophilus" and "Pyrococcus horikoshii", which could indicate that this pathway is more widely spread in prokaryotes than originally proposed.The first and rate-limiting step in the AAA pathway is the condensation reaction between acetyl-CoA and α‑ketoglutarate catalysed by homocitrate-synthase (HCS) (E.C 2.3.3.14) to give the intermediate homocitryl‑CoA, which is hydrolysed by the same enzyme to produce homocitrate.