| Abstract: | Porphyrin synthesis and iron accumulation was stimulated by exogenous 5-aminolevulinic acid (ALA) in uninduced Friend erythroleukemic cells (FELC). Uroporphyrin and protoporphyrin were the major intermediated precursors produced. All porphyrin types were conjugated to protein insoluble cellular components and could be extracted only by methanol sulfuric acid esterification. Heme content of the uninduced FELC was increased 6-fold in the presence of 5 x 10(-4) M ALA. As a consequence, the synthesis of the minor murine hemoglobin component was preferentially induced, an effect similar to that expressed by exogenous hemin. Addition of exogenous ALA to 0.5% DMSO-induced cells increased total hemoglobin synthesis with a higher efficiency of the minor hemoglobin. The endogenous synthesis of porphyrin from exogenous ALA was markedly reduced by hemin. Uroporphyrin, coproporphyrin, protoporphyrin and heme were equally repressed, indicating an inhibitory effect of hemin on ALA dehydrase and urosynthetase activities. In addition, hemin repressed 3H]leucine incorporation into protein by uninduced cells. Incubation of uninduced cells in culture medium without serum in the presence of hemin blocked their protein synthesis activity, whereas addition of serum exerted a protective effect on living FELC. |
