The formation of bilierdin by chicken MACROPHAGE monolayers from protohaemin suspension is UNAFFECTED by CO, and other inhibitors and substances of cytochrome P-450.


2. KCN and NaN3 are potent inhibitors of biliverdin formation from haemin while mepacrine, which inhibits biliverdin formation from haemoglobin, has weak stimulatory properties.


3. Simultaneous phagocytosis of haemin and N-ethylmaleimide-treated red cells containing unlabelled haemoglobin results in stimulation of formation of labelled biliverdin.


4. Microsomal preparation from cultured chicken macrophages which had phagocytosed haemin SUSPENSIONS showed a reduced minusoxidised difference spectrum with a peak at 432 nm, and a trough at 404 nm. The haemoprotein or haemoproteins responsible for this absorption did not react with carbon monoxide. Microsomes from macrophages which had phagocytosed N-ethylmaleimide-treated red cells showed only the difference spectra of strongly bound haemoglobin. In neither case was cytochrome P-450 detected.


5. It is suggested that haemoglobin and haemin are degraded by DIFFERENT PATHWAYS by these cells.