HEME-BIOSYNTHETIC ENZYME-ACTIVITIES AND PORPHYRIN ACCUMULATION IN NORMAL LIVER AND HEPATOMA-CELL LINES OF RAT

The activities of four heme-biosynthetic enzymes, delta-aminolevulinic acid (ALA) synthase, ALA dehydratase, porphobilogen (PBG) deaminase, and ferrochelatase, were studied in five epithelial cell lines of norm al rat liver origin (RL, RLC-10, RLC-24, M, Culb-TC) and five cell lin es derived from Yoshida ascites hepatoma (JTC-1, JTC-2, JTC-15, JTC-16 , JTC-24). The JTC series of hepatoma-derived cell lines exhibited dec reased ALA synthase activity and increased ALA dehydratase activity, a lthough the activities of all four enzymes and the Km values for their respective substrates varied widely from one cell line to another, a finding suggesting that specific regulatory mechanisms for porphyrin m etabolism might operate in each cell type. M cells, which were transfo rmed by 4-dimethylaminoazobenzene in vitro, gave the most abnormal Km values of heme-biosynthetic enzymes among all the cell lines studies, and were found to accumulate hematoporphyrin derivative (HpD).