BIOSYNTHESIS OF HEME AND HEMEPROTEINS IN TISSUE CELLS

IRON INCORPORATION INTO HEME BY PREPARATIONS FROM RAT LIVER

Abstract

1. Incorporation of radioactive iron into heme was observed' by incubating the homogenate of rat liver. Heme was purified either by chroma-tography on celite column or by crystallization. The homogenates of other organs, such as kidney, brain, heart muscle, spleen and voluntary muscle had the similar activity.
2. The product of incorporation after incubating the homogenate with radioactive iron, was firmly bound to the particulate fractions. The heme in mitochondria had high rate of radioactivity. Radioactive hemeproteins were extracted by cholate after the incubation of mitochondria with radioiron. Radioactive heme existed in the fraction of 35-50 per cent ammonium sulfate saturation.
3. The activity to incorporate radioactive iron into heme was found in the particulate fraction of liver cell. The high activity was observed in mitochondrial fraction.
4. The active principle for the incorporation of iron into heme was solubilized from mitochondria with sodium cholate and purified by ammonium sulfate fractionation. The activity was found in the fraction of 50-75 per cent ammonium sulfate saturation.
5. The activity of the cholate extract had the optimum at about pH 7. The incorporation was accelerated by the addition of cysteine. Addition of protoporphyrin did not cause any increase in the incorporation. The activity was totally abolished by heat-treatment.
6. The mechanism of hemeprotein synthesis in liver cell was discussed from the above findings.
The author expresses his cordial thanks to Prof. H. Yoshikawa and Prof. Y. Yoneyama for their kind guidance and encouragement in carrying out this work. Thanks are also due to Drs. Y. Kagawa, Y. Sugita, S. Morimoto and Mr. S. Tanaka of the author's laboratory and Mr. K. Titani, H. Ishikura and K. Taka-hashi of the Department of Chemistry, Faculty of Science for their encouraging discussions.