JBC, Vol. 253, Issue 9, 2954-2962, May, 1978
The green hemoproteins of bovine erythrocytes. II. Spectral, ligand-binding, and electrochemical properties
L. J. DeFilippi and D. E. Hultquist
The two green hemoproteins isolated from bovine erythrocytes (form I and
form II) have been characterized as to spectral, electrochemical, and
chemical properties. The absorption spectra of the isolated hemoproteins
are typical of high spin ferric states. Reduction of the hemoproteins
yields high spin ferrohemoproteins. Complexation of the ferrohemoproteins
with CO and the ferrihemoproteins with cyanide yields low spin complexes,
demonstrating the presence of an exchangeable weak field ligand in both the
ferrous and ferric states of the hemoproteins. The differences in position
and intensity of the absorption peaks of the visible spectra allow the two
forms to be distinguished from one another. The midpoint potential of forms
I and II were found to be +0.075 and +0.019 V, respectively, at pH 6.4 and
+0.038 and -0.005 V, respectively, at pH 7.0. This is consistent with the
gaining of 1 proton/electron during the reduction. The Nernst plot reveals
an unusual 0.5-electron transfer, whereas a quantitative titration
demonstrates a 1-electron transfer. Form I binds cyanide more tightly than
form II (KD of 84 and 252 micrometer, respectively). The observed spectral,
electrochemical, and ligand-binding differences between forms I and II can
be explained in terms of a greater electron-withdrawing ability of the side
chains of the heme of form I relative to the heme of form II.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
