Signal transmission between subunits in the hemoglobin T-state.
To study allosteric mechanism in hemoglobin, a hydrogen-exchange method was used to measure ligand-dependent changes in structural free energy at defined allosterically sensitive positions. When the two alpha-subunits are CN-met liganded, effects can be measured locally, within the alpha-subunit, and also remotely, within the beta-subunit, even though the quaternary structure remains in the T conformation. When the two beta-subunits are liganded, effects occur at the same positions. The effects seen are the same, independently of whether ligands occupy the alpha-chain hemes or the beta-chain hemes. Control experiments rule out modes of energy transfer other than programmed cross-subunit interaction within the T-state. Cross-subunit transfer may depend on pulling the heme trigger (moving the heme iron into the heme plane) rather than on liganding alone.
Englander
J J
JJ
Department of Biochemistry & Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104-6059, USA. joan@HX2.Med.UPenn.Edu
Rumbley
J N
JN
Englander
S W
SW
D003486:Cyanides / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006859:Hydrogen; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D003486:Cyanides; D006454:Hemoglobins; D011994:Recombinant Proteins; D006418:Heme; D006859:Hydrogen