Effect of Hemoglobin and Hematin on Plasma Clearance of Hemopexin,Photo-Inactivated Hemopexin and Albumin 1

Abstract

Summary

The plasma half clearance time (T_1/2) of isotope-labeled rabbit hemo-pexin was 35.5 ± 1.9 hr in rabbits. After intra- and extra-vascular equilibration of ¹²⁵I-hemopexin and ¹³¹I-albumin, injection of either hematin, hemoglobin or methemo-globin (12.5 mg of heme/kg body wt) resulted in the rapid removal of 60-80% of circulating hemopexin (T_1/2 = 7.2 ± 0.6 hr) but did not affect albumin catabolism.

After selective photo-inactivation of hemopexin, the T_1/2 of this hemopexin was comparable to that of the native molecule. However, its plasma disappearance curve was not appreciably affected by administration of hematin.

These findings demonstrate that hemopexin is cleared and catabolized at an enhanced rate during states of plasma heme load, and that modification of critical histi-dine residues of hemopexin eliminates its biological function in plasma heme disposal.