SPIN-LABELED HEMOGLOBIN SUBUNITS

The isolated subunits from human adult hemoglobin and their mercurated derivatives in carbon monoxy form have been spin labeled with N-(l-oxyl-2,2,6,6-tetramethylpiperidinyl)maleimide. The electron spin resonance spectra of the labeled subunits and their various mixtures have been measured at room temperatures. The sedimentation coefficients, the number of the bound labels, and the number of the reactive SH groups have also been determined. The spectra of all the labeled subunits are similar and are very different from that of the spin-labeled tetramer α2β2. The spin label attached to the β93 SH group in the isolated β chains gives a different spectrum from that of the same label attached to the same SH group in the tetramer, indicating that the conformation of the β chains in the isolated form differs from that in the α2β2 tetramer. When the labeled β chains are mixed with native α chains, the spectrum of the former changes very rapidly (within 1 sec) into the spectrum indistinguishable from that of the tetramer. The normally functioning conformation of the β chains is achieved only when they combine with the α chains of different composition. © 1968, American Chemical Society. All rights reserved.