Heme sythesis Functions hemoglobin cytochrome b4 P450 Location of synthesis involves both the mitochondria and the cytosol occurs in nearly every cell occurs in RBC progenitor cells login to view 1 more bullet Pathway ALA synthase is rate limiting enzyme (see above) Deficiencies in heme synthesis hemin occurs when Fe3+ is incorporated instead of Fe2+ porphyria causes login to view 9 more bullets treatment login to view 3 more bullets types login to view 21 more bullets poisoning lead login to view 12 more bullets hexachlorobenzene login to view 4 more bullets iron deficiency iron incorporated in the final step result is microcytic hypochromic anemia see Trace metals topic vitamin B6 deficiency rate limiting enzyme (ALA synthase) requires most commonly due to isoniazid therapy see Vitamins topic Degradation of Heme Function rid body of hemoglobin removed from degraded RBCs Location of degradation spleen site of RBC destruction liver site of bilirubin conjugation intestine conversion by normal gut flora Pathway Bilirubin Properties insoluble must travel in blood bound to albumin conjugation direct (conjugated) login to view 2 more bullets indirect (unconjugated) login to view 2 more bullets Modified forms urobilinogen gives urine yellow color stercobilin gives feces brown color login to view 1 more bullet