FTIR studies of environmental effects on carbonmonoxymyoglobin

In this thesis, Fourier Transform Infrared Spectroscopy (FTIR) was used to study the interaction between the protein myoglobin (Mb), and substrate carbon-monoxide (CO), as a model system of control in protein-ligand systems. IR spectra of the CO molecule bound to Mb have been obtained as a function of intensive variables such as temperature, pressure and pH, as well as in different solvents, and at low hydration. In addition, IR spectra have been obtained for a genetically synthesized version of Mb with glycine substituted for the distal histidine (His E7).The IR spectra of CO bound to Mb consists of four bands labelled A$\sb0$, A$\sb1$, A$\sb2$ and A$\sb3$. The recombination rate of CO to Mb following flash photolysis is different for each band. Control may therefore be exercised at the binding site by changing the relative populations of the bands. It is found that the primary effect of varying the above mentioned thermodynamic variables from their physiological conditions, and of the genetic substitution, is to increase the intensity of A$\sb0$ at the expense of A$\sb1$. It is proposed that the net effect of all these very different perturbations is to disrupt the hydrogen bonds in Mb. This affects the protein on at least two different scales; first, a local scale, in which a specific amino acids residue is affected, altering the binding of CO to Mb through a steric interaction, and second, a global scale, in which hydrogen bonds are disrupted in the bulk of the protein structure, causing a slight change in the conformation of the protein as a whole. This connection between local and global sources of control may be of general significance to protein-ligand systems. It is also found that the temperature dependence of the relative populations of the A states deviates from a Boltzman distribution called the "ankle" can be understood as a temperature-dependent entropy. This also shows that protein has a similar behavior of a glass-forming liquid above the glass temperature.U of I OnlyETDs are only available to UIUC Users without author permissio