The ion pyruvate is the combined base of the pyruvic acid of CH₃-CO-COOH formula.

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Description

The Pyruvate is the finished product of the ways of degradation of the Glucose (the Glycolyse, Voie of pentoses phosphates, way of Entner-Doudoroff). It is the Substrat of the Fermentation in condition Anaérobie, and of the Cycle of Krebs in condition Aérobie.

To become pyruvate in anaérobiose

These reactions take place in the Cytoplasme. In the muscle (for lactic fermentation) or at yeast (for alcoholic fermentation). Others Fermentation S are possible, at the Entérobactérie S. Voir Voies fermentaires enterobacteries.

Lactic fermentation

CH₃-CO-COO^- + NADH + H⁺ <-> CH₃-CHOH-COO^- + NAD⁺

Enzyme: Lactate déshydrogénase

The produced lactate can be regarded as a waste, it is responsible for cramps. However, it can be transported in blood then in the hepatic cells (Cycle of Cory).

Alcoholic fermentation

1. CH₃-CO-COO^- + H⁺ - > CH₃CHO + CO₂ (Enzyme: pyruvate Décarboxylase, in the presence of thyamine pyrophosphate)
2. CH₃CHO + NADH + H⁺ <-> CH₃CH₂OH + NAD⁺ (Enzyme: alcohol Déshydrogénase)

To become pyruvate in aerobiosis

It takes place in the Mitochondrie. The pyruvate penetrates there by the pyruvate translocase. Two reactions are possible which generate the precursors of the Cycle of Krebs:

Oxydative decarboxylation

This reaction is catalyzed by a complex multienzymatic (Pyruvate déshydrogénase) utilizing five Coenzyme S. Three Coenzyme S are related to the apoenzymes: the Thyamine pyrophosphate (or TPP), the Lipoate and FAD (they are prosthetic groupings). The two others are free and nonrelated to the complex: NAD and the Coenzyme have.

ASSESSMENT: Pyruvate + HSCoA + NAD⁺ - > AcétylCoA + CO₂ + NADH + H⁺

The NADH will be then réoxydé by the respiratory Chaîne to produce ATP.

Carboxylation

The reaction is catalyzed in the presence of Biotine by the pyruvate carboxylase (Synthétase), produced oxaloacétate.

ASSESSMENT: Pyruvate + ATP + H₂ + CO₂} - > Oxaloacétate + ADP + P_i

Comparison of the energetic efficiency of the reactions

Starting from a molecule of Glucose (which gives 2 molecules of pyruvate):

• fermentations are less profitable (they release 2 molecules of ATP);
• the uses in aerobiosis release more energy (14 ATP for oxydative decarboxylation, 6 for the carboxylation); and still, it is not finished (see Cycle of Krebs).

See too

• the Glycolysis
• the Way of pentoses phosphates
• the way of Entner-Doudoroff
• the Cycle of Krebs

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