Isolation from erythrocytes of a green hemoprotein with ferroactivator activity

A protein that exhibits ferroactivator activity with purified rat liver P-enolpyruvate carboxykinase was purified to apparent homogeneity from bovine erythrocytes. The homogeneous protein has a molecular weight of 82,000 by high speed sedimentation equilibrium and 90,000 by gel exclusion chromatography. A subunit molecular weight of 22,500 was obtained by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Its isoelectric focusing indicated that the ferroactivator protein has an isoelectric point at pH 5.7. The reduced pyridine hemochrome of the denatured protein shows absorption maxima at 419, 527, and 557 nm which is characteristic of protoheme IX. The native protein is green in color with absorption maxima at 407, 507, and 543 nm. The amino acid composition and immunological studies show that bovine erythrocyte protein is structurally similar to the P-enolpyruvate carboxykinase ferroactivator protein isolated from rat liver. Its function in the erythrocyte is unknown.