C-13 NUCLEAR MAGNETIC-RESONANCE STUDY OF THE MOTIONAL BEHAVIOR OF ETHYL ISOCYANIDE BOUND TO MYOGLOBIN AND HEMOGLOBIN

The interaction of ethyl isocyanide with myoglobin and hemoglobin has been studied by means of 13C nuclear magnetic resonance spectroscopy by using ethyl isocyanide labeled in the ethyl side chain. Chemical shifts, longitudinal relaxation times, and approximate line widths are reported for the resonances of bound [l-13C]ethyl isocyanide (CH313CH2NC) and bound [2-13C]ethyl isocyanide (13C-H3CH2NC), as well as nuclear Overhauser enhancement values for the latter compound. Bound [1-13C] ethyl isocyanide shows a chemical shift which is practically the same for sperm whale myoglobin, harbor seal myoglobin, and human hemoglobin. The same is true for bound [2-13C]ethyl isocyanide. This suggests that the heme environment experienced by the ethyl side chain of ethyl isocyanide is similar in harbor seal myoglobin, sperm whale myoglobin, and the liganded (R) form of human hemoglobin. A theoretical analysis of the longitudinal relaxation time and nuclear Overhauser enhancement data, by using the restricted diffusion model [Wittebort, R. J., & Szabo, A. (1978) J. Chem. Phys. 69, 1722-1736; London, R. E„ & Avitabile, J. (1978) J. Am. Chem. Soc. 100, 7159-7165], reinforces this conclusion. It suggests that the motion of the ethyl group of bound ethyl isocyanide is somewhat restricted and that the motional behavior and degree of restriction of motion may be similar for myoglobin and the R state of hemoglobin. © 1979, American Chemical Society. All rights reserved.