A protein modulator of erythrocyte membrane (Ca2+ + Mg2+)-ATPase inhibitor protein |
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Affiliation: | Department of Biochemistry, University of Hong Kong, Sassoon Road, Hong Kong Hong Kong |
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Abstract: | A protein modulator of erythrocyte membrane (Ca2+ + Mg2+)-ATPase inhibitor protein was purified to apparent homogeneity from pig membrane-free hemolysate by a combination of carboxymethyl-Sephadex chromatography, gel filtration, chromatofocusing (pH 7-4) and subsequent removal of trace inhibitor protein by salt treatment. Gel filtration gave a molecular weight of 57 500 for the purified protein modulator, while SDS-polyacrylamide gel electrophoresis of dithiothreitol-treated modulator revealed one single band with a molecular weight of 29 000. Isoelectric focusing of the dithiothreitol-treated protein revealed one band (isoelectric pH 4.85), while untreated modulator gave an extra band (isoelectric pH 4.96). It contains no methionine and has an acidic content 73% higher than that of its basic residues. Freshly prepared or dithiothreitol-treated modulator suppressed both pig and human erythrocyte (Ca2+ + Mg2+)-ATPase inhibitor protein activity, but did not affect ATPase and calmodulin activities. Modulator-coupled Affi-Gel 15 could be employed for purification of the protein inhibitor. |
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