Cyclus acidi citrici

Cyclus acidi citrici vel cylcus acidorum triclyclicorum vel tricarboxylici acidi cyclus vel cyclus Krebs est iter metabolicum intracellulare et iter paenultimum in mitochondriis, ante phosphorylationem oxydativam enim, energiam cellularem (ATP) generantem.

Cyclus ex pyruvato et, non exigue, aqua generat duo substantias, electrona e^- in proximum iter portantes: NADH+H⁺ et FAD(2H).

Hic cyclus anno 1937 ab Iohanne Adolpho Krebs primo descriptus est; nimirum Krebs anno 1953 praemium Nobelianum physiologiae et medicinae addictum est^[1]. Hac de causa cyclus non raro "cyclus Krebs" appellatur. Praeterea nomen "cycli acidorum tricyclicorum" de tribus acidis tricyclicis intra cyclum Krebs (citrato, aconitato, isocitrato) partibus cursus cycli sumitur; denique nomen "cycli acidi citrici" de molecula acidi citrici, non electrice onerati, derivatur, quamquam citratum forma electrice onerata partem cycli ipsius capit.

Aequatio generalis cycli Krebs:

Acetylo-CoA + 3 NAD⁺ + FAD + GDP + P_i+ 2 H₂O → CoA + 3 NADH + 3 H⁺ + FAD(2H) + GTP + 2 CO₂

Nota cycli Krebs ope, nec oxygenium consumatur, nec ATP generetur, sed generentur GTP et CO₂. Oxygenium quidem, ut ATP, demum in itinere proximo, phosphorylatione oxydativa, momenta maxima habebit.

• Substrata pyruvatum generantia
• Aqua (cyclo 2 moleculae)
• Mitochondria sana

• Reactio biochemica 0/10 (Citrati synthasis): Oxaloacetatum + Acetylo-CoA + H₂O → Citratum + CoA-SH
• Reactio biochemica 1 (Aconitasis): Citratum + CoA-SH → cis-Aconitatum + H₂O
• Reactio biochemica 2 (Aconitasis): cis-Aconitatum + H₂O → Isocitratum
• Reactio biochemica 3 (Isocitrati dehydrogenasis): Isocitratum + NAD⁺ → Oxalosuccinatum + NADH + H⁺
• Reactio biochemica 4 (Isocitrati dehydrogenasis): Oxalosuccinatum → α-Ketoglutaratum + CO₂
• Reactio biochemica 5 (α-Ketoglutarate dehydrogenasis): α-Ketoglutaratum + NAD⁺ + CoA-SH → Succinylo-CoA + NADH + H⁺ + CO₂
• Reactio biochemica 6 (Succinylo-CoA synthetasis): Succinylo-CoA + GDP + P_i → Succinatum + CoA-SH + GTP
• Reactio biochemica 7 (Succinati dehydrogenasis): Succinatum + Ubiquinonum (Q) → Fumaratum + Ubiquilonum (QH₂)
• Reactio biochemica 8 (Fumarasis): Fumaratum + H₂O → L-Malatum
• Reactio biochemica 9 (Malati dehydrogenasis) L-Malatum + NAD⁺ → Oxaloacetatum + NADH + H⁺
• Reactio biochemica 10/0 (Citrati synthasis): Oxaloacetatum + Acetylo-CoA + H₂O → Citratum + CoA-SH

• Electrona (cyclo 3 moleculae NADH+H⁺, 1 molecula FAD(2H))
• GTP (cyclo 1 molecula)
• CO₂ (cyclo 2 moleculae, aeris exspirati)
• Succinylo coenzymum A in parte in synthesem porphyrini defertur.

• Jean-Jacques Brière 1, Judith Favier, Anne-Paule Gimenez-Roqueplo, Pierre Rustin. "Tricarboxylic acid cycle dysfunction as a cause of human diseases and tumor formation", Review Am J Physiol Cell Physiol, 2006ː C1114-C1120
• Gray, L.R., Tompkins, S.C. & Taylor, E.B. "Regulation of pyruvate metabolism and human disease". Cell. Mol. Life Sci., 2014ː 2577–2604
• Oliver E. Owen, Satish C. Kalhan, Richard W. Hanson. "The key role of Anaplerosis and Cataplerosis for Citric Acid Cycle Function", The Journal of biological Chemistry, 2002ː 30409-30412
• Mulchand S. Patel, Natalia S. Nemeria, William Furey and Frank Jordan. "The Pyruvate Dehydrogenase Complexes: Structure-based Function and Regulation", Journal of biological Chemistry, 2014: 16615–16623

• Acidum fumaricum
• Energia
• Mitochondrium

• Khan academy de cycli acidi citrici. (Anglice)
• Alii cursus cycli Krebs. (Anglice)

Haec stipula ad biologiam spectat. Amplifica, si potes!