The stability of the heme-globin linkage : measurement of heme exchange

Publisher Summary Heme transfer was first measured from ferrimyoglobin to organic bases, such as histidylhistidine and pilocarpine and then used apomyoglobin as the acceptor for the hemes of Hb + . The values for the association constant thus obtained ranged from 10 12 to 10 16 . This chapter discusses the heme exchange between different ferrihemoglobins and heme transfer to serum albumin after separating the products by ion-exchange chromatography. Heme transfer is followed from ferrihemoglobin to the plasma hemebinding protein—hemopexin. The method for heme transfer from Hb + to serum albumin under conditions can be followed spectrophotometrically. It is exceedingly simple and readily yields information on both the equilibrium and the kinetic stability of the heme-globin linkage. The measurements are based on the fact that the well-known change in the spectrum of ferrihemoglobin, which accompanies the loss of a proton from the Fe 3+ -linked water molecule, with a p K of 8.2, is absent in methemalbumin (MHA). Therefore, although the spectra of these two heme proteins are quite similar in neutral and acid solution, they show a large difference with increasing pH.