Keto acid

Keto acids, complete, often referred keto carboxylic acids in the German language as oxo acids are carboxylic acids containing an additional carbonyl group. Their characteristics are influenced by the distance of the two functional groups. The distance often referred to by Greek letters ( α - ever = adjacent or vicinal, β - ever - distance = 1.3, etc.).

Biochemistry

Keto acids play in cellular processes a central role in amino acid metabolism and in the maintenance of redox status. α - keto acids, the carbon skeleton of the α - amino acid analogue. β -keto acids are high-energy (unstable ) metabolites, readily undergo reactions with loss of CO2 ( decarboxylation).

α -keto acids

Pyruvic acid and its salts, the pyruvate is the simplest α -keto acid. Under the action of a pyruvate decarboxylase pyruvic acid can be decarboxylated during alcoholic fermentation to acetaldehyde ( and CO2 ) or in the multi-enzyme complex of pyruvate dehydrogenase to acetyl -CoA ( and CO2). In the citric acid cycle, there is another reaction on the same basic principle: the decarboxylation of α - ketoglutarate to succinyl -CoA. Coenzymes of these processes, referred to as " oxidative decarboxylation " are thiamine pyrophosphate and NAD , possibly coenzyme A. Under anaerobic conditions, pyruvate is reduced to lactate in the mammalian organism (eg in muscle during intensive use ).

In vitro, a similar reaction can be observed: The relatively weak C -C bond in the group R -CO- COOH, can be cleaved by the addition of concentrated sulfuric acid, and generates carbon monoxide and the corresponding carboxylic acid R -COOH.

Another typical reaction of α -keto acids, the transamination which includes a reciprocal amination with simultaneous deamination of glutamic acid, without free ammonia occurs. Thus, alanine from pyruvate, oxaloacetate from ( a compound that α - and β -keto acid is at the same time ) aspartate and glutamate from α -ketoglutarate, coenzyme pyridoxal phosphate.

β -keto acids

The simplest β -keto acid is the fickle acetoacetic acid. β -keto acids are usually unstable substances which decompose to decarboxylation. This process can be spontaneous, biochemical also catalyzed in the cell run. An example is the decarboxylation of oxaloacetate in the gluconeogenesis by phosphoenolpyruvate carboxykinase ( PEP CK ) or the malic enzyme (ME). Acetoacetic acid decomposes into acetone and carbon dioxide.

γ -keto acids

The simplest γ -keto acid is levulinic acid.