Studies on Hemoglobin Metabolism. I. The Kinetic Properties of the Plasma Hemoglobin Pool in Normal Man*

Disposal of plasma heme in normal man and patients with intravascular hemolysis

“…The plasma half-life of the haptoglobin-hemoglobin complex in man when studied with tracer amounts of hemoglobin has been estimated to be as short as 10-30 min (18,41), although ti values of 2-4 hr have been reported in studies in which larger amounts of hemoglobin were administered (16,17). On the basis of a few studies in man, it appears that free hemoglobin is cleared even more rapidly than the haptoglobinhemoglobin complex (17,42).…”

“…The clearance kinetics and organ sites of removal of plasma hemoglobin have been studied by a number of investigators (15)(16)(17)(18)(19), and the reutilization of hemoglobiniron characterized (20). Little is known, however, of the early steps in the catabolism of plasma heme.…”

Iron Absorption. Iv. The Absorption of Hemoglobin Iron*

“…While it is theoretically possible that after absorption hemoglobin or heme (or a fragment of heme) might be bound directly to plasma proteins and be processed by the reticuloendothelial tissues at some distant site, this possibility was not supported by the finding that the absorbed iron in plasma behaved as transferrinbound iron. If it had entered the plasma as hemoglobin, a detectable amount would have been found in nondialyzable form, since the half-time of plasma hemoglobin turnover is of the order of 20 minutes (23).…”

Genetic variants and cell-free hemoglobin processing in sickle cell nephropathy

“…Under normal conditions, plasma cell-free hemoglobin represents approximately 10% of the hemoglobin from red blood cell turnover 18 (average concentration 0.2 μM, range <0.06-0.7). 19 Intravascular hemolysis that exceeds the ability of haptoglobin and haptoglobin-related protein-ApoL1 complexes to bind cell-free hemoglobin results in hemoglobinuria 20 and, based on animal models, cell-free hemoglobin-mediated damage to the proximal tubule may be a mechanism of kidney damage.…”