Decarboxylation

Decarboxylation, the removal of CO₂ from the carboxyl group (COOH) of organic acids, plays an important role in the processes of putrefaction and in intermediate metabolism. Under the influence of putrefactive bacteria, as a result of decarboxylation, various amino acids according to the scheme: R - CH₂ - NH₂ - COOH → R - CH₂ - NH₂ + CO₂ form amines, often possessing a pronounced physiological effect; thus, from tyrosine is formed tyramine, which strongly increases blood pressure, similar to adrenaline; histidine gives histamine upon decarboxylation (see also Putrefaction). In the processes of fermentation, through decarboxylation (after preliminary deamination), from leucine is formed amyl alcohol (see). Decarboxylation apparently plays a particularly important role in the processes of intermediate metabolism. According to modern views, the CO₂ released during both aerobic (respiration) and anaerobic metabolism (fermentation) is formed not by the direct oxidation of carbon, but through the decarboxylation of carboxyl groups formed as a result of oxidation-reduction processes. A prototype of such a process is the splitting of pyruvic acid under the influence of the enzyme carboxylase: CH₃ - CO - COOH → CH₃ - CHO + CO₂, or the decarboxylation of oxaloacetic acid: COOH - CO - CH₂ - COOH → COOH - CO - CH₃ + CO₂.