Clearance of certain modified haptoglobins from the rabbit circulation

1. Human haptoglobin (Hp) type 2-1 was subjected to the sulfanilazo-modification of tyrosine and histidine residues, the removal of sialic acid, and the reduction of disulfide bonds (isolation of alpha 2, alpha 1, beta subunits), respectively. Radioactively labeled preparations were administered intravenously to rabbits. 2. Human Hp and isolated beta (heavy) chain disappeared from the circulation somewhat faster (half-lives = 72 and 67 h, respectively), than homologous rabbit Hp (half-life = 96 h). Hp light chains (alpha 2, alpha 1), devoid of oligosaccharide showed shorter half-lives of 27-19 h. 3. Treatment of Hp with diazotized sulfanilic acid resulted in an appreciable reduction of half-life to 21-11 h, as dependent on the number of modified residues. 4. Asialo-Hp, asialo-beta chain, and asialo-sulfanilazo-Hp were cleared rapidly from the circulation with half-lives of 5.5, 5.0, and 4.2 h, respectively. 5. These results suggest that in different pathways of Hp catabolism in vivo, polypeptide recognition markers in addition to carbohydrate ones, are involved.