SPIN-LATTICE RELAXATION OF DENATURED NITROSYL HEMOPROTEINS

The temperature dependence of the spin-lattice relaxation of denatured nitrosyl hemoglobin (HbNO), nitrosyl myoglobin, powdered HbNO, and he matin-NO was studied between 4 and 70 K. The results were fitted with both T-n and e(-Delta/T) models. In the first model, the relaxation is mediated by tunneling modes of a two-level system, A correlation betw een the n values and the functional state of the protein was observed, The striking coincidence of the range of the low-lying energy level a nd the temperature range where EPR spectra change suggests the existen ce of two conformations of the bound heme. The importance of the prese nce and structure of the globin is revealed in the difference between relaxation parameters of native proteins, denatured proteins, and hema tin. (C) 1996 Academic Press, Inc.