X-ray and EPR studies of strong intermolecular sickle hemoglobin contacts

Both 4-maleimido-2,2,6,6-tetramethyl-1-piperidinyloxy (Mal-6) spin labeled deoxy hemoglobin A and 3-maleimido-2,2,5,5- tetramethyl-1-pyrrolidinayloxy (Mal-5) spin labeled deoxy hemoglobin A were crystallized and their crystal structures were solved. The crystal structure of Mal-5 spin labeled deoxy hemoglobin A was solved at a resolution of 1.84 A with an R factor of 15.83%; the crystal structure of deoxy Mal-6 spin labeled hemoglobin A was solved at a resolution of 2.10 A with an R-factor of 15.12%. The 5-member maleimide rings of both the Mal-5 and Mal-6 spin labels were covalent bond to the ;Conventional EPR and saturation transfer EPR studies have been performed at 9 and 35 GHz, and theoretical spectra have been simulated. The best fit parameters for these spectral simulations indicate that the characteristic time for loss of Z-axis correlation with the external magnetic field is approximately 10;The crystal structure of Mal-6 spin labeled deoxy hemoglobin A was superimposed with that of hemoglobin S at a resolution of 3.0 A, as solved by Padlan and Love (1985a). The orientation of the magnetic Z-axis of the Mal-6 spin label is...