The Use of Reticulocytes with High Non‐haem Iron Pool for Studies of Regulation of Haem Synthesis*

TLDR: One‐hour incubation of reticulocytes with 10−2m isonicotinic acid hydrazide (INH) and transferrin‐bound 59Fe changes the normal distribution of radioiron inside the cell, which is considered as further evidence for the inhibitory effect of haem on the membrane transport of iron.

Abstract: Summary One-hour incubation of reticulocytes with 10−2m isonicotinic acid hydrazide (INH) and transferrin-bound 59Fe changes the normal distribution of radioiron inside the cell. About 10% of 59Fe is found in haem and 90% is present in the non-haem iron pool. The accumulated non-haem radioiron may be utilized for haem synthesis. This is demonstrated by the reincubation of washed reticulocytes with a high non-haem radioiron pool induced by INH under optimal conditions. The incorporation of radioiron from intracellular non-haem pool into haem is used as a method for the estimation of the rate of haem synthesis in the presence of various inhibitors. INH reduces haem synthesis from non-haem iron to a greater extent than that from transferrin iron. On the other hand, haemin, which inhibits the incorporation of 59Fe from transferrin into haem, does not significantly decrease the utilization of intracellular non-haem iron for haem synthesis. These results are considered as further evidence for the inhibitory effect of haem on the membrane transport of iron. Cells with an artificially increased non-haem iron pool incorporate more [2-14C]glycine into haem than normal reticulocytes. These results are in accordance with the possibility that the supply of iron to the critical sites of haem synthesis may be a limiting factor controlling the rate of haem synthesis.