Mitochondria biosynthetic enzymes

As a result of such methods it was concluded that four of the eight enzymes of the heme biosynthetic chain are localized inside the inner membrane of the mitochondrion, whereas the other four enzymes reside in the cytosol. 

The final step in the formation of heme is the insertion of iron into protoporphyrin. This function is performed in the mitochondrion. It suggests that heme, the end product of the biosynthetic chain, would be ideally situated to act as an allosteric end-product inhibitor of the first enzyme, ALA-synthetase. No satisfactory evidence has yet been obtained, however, that the activity of mitochondrial ALA-synthetase is inhibited directly by heme, except when heme is added in concentrations which appear to us too high to be considered physiological. For example, even soluble ALA-synthetase isolated from mitochondria required Q M heme to inhibit the activity 77% [Bottomley and Smithiee, 32]. Whether the free heme in mitochondria could attain these high concentrations could be determined on mitochondria isolated from ALA-treated cells. Another problem that requires study is the... 

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