Uncomplexed haem suppresses the proliferation of human erythroleukemia (HEL) cells, the effect of which can be partially reversed by apo-haemopexin. The process of suppressed proliferation is paralleled by differentiation of the HEL cells accompanied by haemoglobin synthesis. Equivalent amounts of haem supplied to the cells in the form of haem-haemopexin neither affected their proliferation nor promoted haemoglobin synthesis. Haemopexin internalization by HEL cells only occurred if the haem-haemopexin complexes were continuously supplied to the cells at 37 °C. It suggests that fluid flow endocytosis rather than receptor mediated endocytosis is operative in this process.

Keywords: haem, haemopexin, HEL, proliferation, receptor