Catabolism of heme moiety of hemoglobin.haptoglobin in rat liver cells in vivo.

After intravenous administration of [3H-heme,14C-globin]hemoglobin.haptoglobin or [59Fe-heme]hemoglobin.haptoglobin to rats, the radioactive materials extracted from the liver homogenate or its subcellular fractions were subjected to a gel filtration column. In addition to the 82-kDa component, we found three metabolites of heme moiety of the complex in the subcellular fractions. Intact hemoglobin.haptoglobin complex with 3H, 14C, and 59Fe radioactivities, an 82-kDa component with 3H, 14C, and 59Fe radioactivities, a 40-kDa component with 3H and 59Fe radioactivities, a lower molecular weight component with 3H and 59Fe radioactivities, and a component with 3H and 59Fe radioactivities bound to the microsome, which are referred to as peaks A, B, C, D, and E, respectively. Using a differential centrifugation technique, most of peak B was found in the mitochondria-lysosomal fraction. Peaks C and D were in the 82,500 x g supernatant fraction, while peak D was also found in the mitochondria-lysosomal fraction. The molecular weight of peak C was approximately 40 kDa, and the 3H radioactivity of peak C was eluted at the same fraction as glutathione S-transferases using both gel filtration and ion exchange chromatography. Peak E that was solubilized from the microsomes was found at the microsomal heme protein fraction on gel filtration chromatogram. Some of the 3H radioactivity in the microsomes was partially co-purified with cytochrome b5 fraction. These results indicate that there are at least four metabolites of heme moiety of hemoglobin.haptoglobin complex in rat liver cells during its catabolism and suggest that some of the heme derived from catabolized hemoglobin.haptoglobin complex binds to glutathione S-transferases in the cytosol and is incorporated into apoheme proteins in the microsomes or at least apocytochrome b5.