14CO2‐Bildung aus [3‐14C]Serin in roten Blutzellen

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Abstract
Substrate‐free incubated erythrocytes and reticulocytes of rabbits form 14CO2 from [3‐14C]‐serine. The 14CO2 formation from [3‐14C]serine exhibits a maturation‐dependent maximum, which is about ten times higher than that of erythrocytes. The production of 14CO2 from [3‐14C]serine requires the splitting off of the hydroxymethyl group with formation of glycine. Serine undergoes neither desamination nor transamination. This is indicated by the fact that neither pyruvate, nor lactate or alanine are labelled. The β‐carbonatom of [3‐14C]serine is found in the porphyrines and the 14CO2 formed from serine is diluted by inactive formate. In erythrocytes the 14CO2 is formed exclusively from formate by the peroxidative action of catalase. If catalase is irreversibly inhibited with 3‐amino‐1,2,4‐triazole the 14CO2 formation from [3‐14C]serine, is completely suppressed. In reticulocytes there exists a second catalase‐independent pathway of 14CO2 formation from [3‐14C]serine, which is proposed to be as follows: condensation of formyl‐tetrahydrofolate with succinyl‐CoA with formation of α‐ketoglutar‐semialdehyde, its oxidation to α‐ketoglutarate and oxidative decarboxylation to succinate. This pathway is indicated by the dilution of 14CO2 from [3‐14C]serine by glycine and particularly by the incorporation of the β‐carbon‐atom of serine in α‐ketoglutarate.