Hemin-mediated oxidative degradation of proteins

Hemin, in the presence of 2-mercaptoethanol and oxygen, catalyzes the selective degradation of heme-binding proteins to small peptide fragments. Among the proteins examined, the heme-binding protein of rabbit serum (HBP-93) proved to be unusually sensitive. Myoglobin also exhibited considerable sensitivity whereas hemopexin and bovine serum albumin were only slightly susceptible to this degradative action of hemin. The reaction with HBP-93 dependend upon coordination of the protein with hemin, was optimal at pH 6.5 and increased 4-fold as the temperature was elevated from 10 to 60°C. The requirement for both oxygen and the reducing agent, 2-mercaptoethanol, and the partial protection of HBP-93 to degradation by catalase, superoxide dismutase, mannitol, and thiourea suggest the involvement of reduced oxygen species in the reaction. A possible role for the heme-mediated degradation of proteins in cell differentiation and other biological responses is discussed.