Principles of Biochemistry (2+1)

3.5.2 Fates of Pyruvate

The production of pyruvate from glucose (glycolysis) occurs in a similar manner in most cells. In contrast, the fate of the pyruvate so produced varies with cellular conditions and the nature of the organism. Three common fates for pyruvate are of prime importance: conversion into acteyl CoA, lactate, and ethanol.

1. Oxidation to Acetyl CoA

Under aeriobic conditions, pyruvate is oxidized to acetyl CoA catalyzed by pyruvate dehydrogenase. 

2. Formation of Lactate

Pyruvate is converted in to lactate by the action of lactate dehydrogenase in the presence of NADH + H⁺ .  NAD⁺ is formed.  

3. Ethanol Fermentation

Ethanol fermentation is the enzymatic anaerobic conversion of pyruvate to ethanol and carbon dioxide. 

The first step is conversion of pyruvate to ethanol in a decarboxylation reaction to produce acetaldehyde.

 

Second step involves reduction of acetaldehyde to produce ethanol.

A key concept in considering these fates of pyruvate is the need for a continuous supply of NAD⁺ for glycolysis. As glucose is oxidized to pyruvate in glycolysis, NAD⁺ is reduced . It is significant that each pathway of pyruvate metabolism includes provisions for regeneration of NAD⁺ from NADH so that glycolysis can continue.