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N-terminal spin label studies of hemoglobin, Ligand and pH dependence.
Metadata
JournalBiochim. Biophys. ActaNot FoundDate
1975-Nov-18
Publication Type
Journal Article
Volume
1975-Nov-18 / 412 : 187-93
Author
Giangrande M , Kim YW , Mizukami H
DoiPMIDMESH
Electron Spin Resonance Spectroscopy
Hemoglobins
Humans
Hydrogen-Ion Concentration
Ligands
Male
Oxyhemoglobins
Protein Conformation
Spectrophotometry
Spin Labels
Abstract
Human hemoglobin was spin labeled with 4-isothiocanato-2,2,6,6-tetramethyl-piperdinooxyl, which is known to bind specifically to the N-terminal alpha-amino groups of proteins and slightly to the reactive sulfhydryl groups. Electron spin resonance (ESR) analysis indicated a partially resolved five-line spectrum, suggesting that the label was attached to at least two different binding sites. Using specific blocking reagents prior to spin labeling, the two binding sites were attributed to the sulfhydryl group of beta-93 (immobile) and the alpha-amino group of the N-terminal valines (mobile). The relative motion of the spin at one set of binding sites was restricted regardless of the state of ligation and pH, while the motion at the other site showed dependence on those parameters, e.g. the spin-labeled N-terminal ends of deoxyhemoglobin have restricted motion at all pH ranges studied, while those of oxyhemoglobin are relatively free to move at the basic pH range, but become more restricted in the acidic pH range.
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