Inhibitory effect of plasma on photohaemolysis in erythropoietic protoporphyria.

The effect of plasma and serum on the photohaemolysis of red cells from erythropoietic protoporphyria patients was studied. Low concentrations (up to 50-100 ml/l) markedly inhibited the rate of photohaemolysis, this effect being partially reversed at higher plasma concentrations. Most of the lysis-inhibiting material co-eluted with serum albumin on gel filtration columns, although a considerable inhibiting effect was also associated with higher molecular weight material. A significant part of the albumin effect can be ascribed to its protoporphyrin-binding capacity. However, most of the effect seems due to an as yet unidentified property of this protein. Evidence is presented that the effect of albumin must be somehow specific to the human protein, as albumins from other sources were much less effective.