Interaction of rabbit hemoplexin with copro- and uroporphyrins.
Rabbit hemopexin forms equimolar complexes in vitro with the I and III isomers of both coproporphyrin and uroporphyrin. The apparent dissociation constants (Kd) of these complexes are estimated to be 4-10(-7) M for coproporphyrin-hemopexin and 10(-6) M for uroporphyrin-hemopexin by equilibrium dialysis and quenching of protein fluorescence. Results of competitive binding experiments suggest that all four porphyrins bind at the heme-binding site of hemopexin, and that the relative affinity of rabbit hemopexin for these porphyrins is: deuteroheme greater than coproporphyrin I or III greater than uroporphyrin I or III. These findings provide further evidence that hemopexin may function as a transport protein for circulating coproporphyrins as well as for heme.
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D003306:Coproporphyrins; D006466:Hemopexin; D007700:Kinetics; D011166:Porphyrins; D011485:Protein Binding; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D014578:Uroporphyrins
D003306:Coproporphyrins; D011166:Porphyrins; D014578:Uroporphyrins; D006466:Hemopexin