Isolation of the haemopexin‐haem receptor from pig liver cells

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Abstract
Isolated pig liver plasma membranes interact specifically with the haemopexin‐haem complex (K d 4.4 × 10−7 M). Affinity chromatography was used to isolate a membrane component which binds this complex with high affinity. Pig serum haemopexin was first isolated by affinity chromatography on haemin‐Sepharose followed by HPLC gel filtration. Liver membranes solubilized with Triton X‐100 were incubated with haemin‐Sepharose saturated with haemopexin, and as a control, with affinity gel lacking haemopexin. SDS‐polyacrylamide gel electrophoresis of the eluted protein indicated that from the haemin‐Sepharose emerglow‐molecular‐mass haemin‐binding proteins whereas the eluate from haemopexin‐haemin‐Sepharose contained an additional 71 kDa protein, which did not bind free haemin. This protein appears to represent the haemo‐pexin‐haem receptor or a part of it. Haem from the haemopexin complex, as also free haemin, was accepted by a binder in the plasma membrane, which in gel filtration behaved like an 80 kDa molecule. This component probably represents a second functional subunit of the haemopexin‐haem receptor.