Studies on Modified Hemoglobins
Year: 1971
Type: article
Abstract: The pH dependencies of the spin state equilibria of ferric hemoglobin, of isolated o( and /? subunits, and of a semihemoglobin were investigated by measurements of paramagnetic susceptibilities at 293" K and 77" K, visible absorption spectra at 293" K and 77" K, and electron paramagnetic resonance spectra (EPR) at 77" K and 4.2' K. Similar results were obtained by all three methods.Acid ferric forms of hemoglobin, LY chains, and semi-hemoglobin, which were in the high spin state at 293" K, were reversibly converted to a mixture of high spin and low spin compounds upon cooling to 77" K. Acid ferric /3 chains were a mixture of high spin and low spin compounds at 293' K and in an essentially low spin state at 77" K.The low spin compound formed in these preparations was not detected by EPR at 77" K but showed EPR signals at g, = 2.75, g2 = 2.25, and g, = 1.69 at 4.2" K. On the basis of its optical and EPR characteristics, the low spin compound was assigned a structure in which the 6th coordination position of the heme iron is occupied by a nitrogenous group, probably by the distal histidyl residue.It was proposed that the conformational constraint exerted by the loss of the a-/3 subunit contacts in the /3 chains and the steric hindrance caused by frozen media might be responsible for the proposed bonding of the distal group directly to the heme iron.It has been assumed on the basis of the magnetic susceptibility at room temperature (3) and the electron paramagnetic resonance spectra at low temperatures (4) that acid Hb+ is a purely high spin compound under both conditions.However, Iizuka
Source: Journal of Biological Chemistry
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W1586590993