Is There a Heme-Stimulating Factor in Human Plasma? ∗

Summary

(1) Nakao et al.(6) have suggested that plasma samples from a variety of hematological disorders possess heme-stimulating activity as compared to normal plasma. This activity was determined by an in vitro technique in which radioiron was used to measure heme synthesis. (2) The present studies have shown that any marked increase in heme formation, determined by the same technique, could be explained by diminution of the residual iron-binding capacity of the plasma sample. (3) In further experiments the residual iron-binding capacity of normal human plasma was modified by addition of varying amounts of non-radioactive iron. Heme formation in the presence of the plasma was directly related to degree of saturation of the residual iron-binding capacity. (4) It is concluded that no definite evidence has yet been obtained for the presence of a specific heme-stimulating factor in human plasma.