Biosynthesis of C14-labeled amino acids by Chlorella ellipsoidae

The usefulness can hardly be overemphasized of radioactive amino acids in biochemical researches. The preparation of all kinds of labeled natural amino acids by purely chemical synthesis is undoubtedly a time-consuming, laborious task. Frantz et al.((2)) recommended the use of autotrophic bacteria for the preparation of C-14 labeled amino acids, i.e. the biosynthesis from C-14 carbon dioxide by Thiobacillus thiooxidans. Schieler et al.((4)) developed a procedure for the biosynthesis and isolation of C-14 amino acids by means of photosynthesis by Chlorella pyrenoidosa. However, they used non-labeled glucose in addition to (CO2)-O-14 as the carbon source. Thus the amino acids which they obtained were not uniformly labeled. The present authors intended not only to prepare C-14-labeled amino acids by biosynthesis but also to estimate amino acid contents of the Chlorella protein by the use of uniformly C-14-labeled protein. Chlorella ellipsoidae was cultivated with (CO2)-O-14 as the sole carbon source and the protein was isolated in a usual way. This was hydrolyzed with hydrochloric acid and the amino acids were separated by ion-exchange chromatography. From the radioactivity of the fractions corresponding to each amino acid the relative amounts could be roughly estimated.