A.B., Brandeis University
Ph.D., University of California at Los Angeles
The aim of our research is to contribute to an understanding of the catalytic mechanisms of the heme enzymes known as peroxidases, catalases and cytochromes P-450 via resonance Raman spectroscopy. Cytochrome P-450 is an enzyme that is believed to be involved in deleterious side reactions that cause the activation of certain substances into carcinogens. Examples of these substances are polycyclic aromatic hydrocarbons, which have only recently (on the evolutionary timescale) achieved elevated concentrations within the environment. Postulated intermediate enzymatic states in the mechanism of cytochrome P-450 that involve the heme in high oxidation states and appear to be critical to the cytochrome P-450 mechanism have not yet been spectroscopically accessible. Direct studies of the cytochrome P-450 intermediates may not yet be practical and await further developments. However, the intermediate states of the related enzymes known as peroxidases and catalase have been under intensive study since the 1940s. Investigations of the cytochrome P-450 mechanism have, therefore, focused on the various peroxidase and catalase enzymes, along with synthetic models.
The Raman effect is manifested by shifts in frequency, up and down, of light scattered inelastically by a chemical substance. These frequency shifts correspond to the internal molecular vibrations of that substance. Previously the primary method for vibrational identification of organic and inorganic compounds, after World War II it was superseded by infrared absorption spectroscopy. Raman spectroscopy experienced an important resurgence in the 1960s upon the invention of the laser. It presents many advantages for biological samples because of the resonance enhancement effect and because water gives only a very minor interference. The resonance Raman effect allows selective enhancement of signals from chromophoric groups within a molecule, and the resultant enhancement provides high sensitivity to features with very low concentrations. The intermediates of peroxidase and catalase are typified by two highly oxidizing enzymatic states known as compounds I and II, which respectively are two and one oxidizing equivalents above the resting enzyme. Compound II contains the heme iron in the Fe(IV) state (ferryl), while compound I contains the ferryl heme with an additional electron removed from the porphyrin ring. Over the past several years our laboratory has been involved in resonance Raman studies of horseradish peroxidase and related enzymes such as ferryl myoglobin and cytochrome c peroxidase. Though our major findings have arisen from studies of the ferryl type intermediates (compound II of horseradish peroxidase and lactoperoxidase, compound ES of cytochrome c peroxidase, etc.) we have recently been able to resolve resonance Raman signals from the elusive compound I intermediates of horseradish peroxidase and chloroperoxidase.
Updated October 2010
“Microwave Synthesis of Graphene Sheets Supporting Metal Nanocrystals in Aqueous and Organic Media” Hassan M. A. Hassan, Victor Abdelsayed, Abd El Rahman S. Khder, Khaled M. AbouZeid, James Terner and M. Samy El-Shall. (2009) J. Mater. Chem 23: 3832-3837.
Torres, I.P.; Terner, J.; Pittman, R.N.; Proffitt, E.; Ward, K.R., Measurement of hemoglobin oxygen saturation using Raman microspectroscopy and 532-nm excitation. Journal of Applied Physiology 2008, 104, 1809-1817.
Gruia, F.; Ionascu, D.; Kubo, M.; Ye, X.; Dawson, J.; Osborne, R.L.; Sligar, S.G.; Denisov, I.; Das, A.; Poulos, T.L.; Terner, J.; Champion, P.M., Low-frequency dynamics of Caldariomyces fumago chloroperoxidase probed by femtosecond coherence Spectroscopy. Biochemistry 2008, 47, 5156-5167.
Osborne, R.L.; Coggins, M.K.; Terner, J.; Dawson, J.H., Caldariomyces fumago chloroperoxidase catalyzes the oxidative dehalogenation of chlorophenols by a mechanism involving two one-electron steps. Journal of the American Chemical Society 2007, 129, 14838-14839.
Ward, K.R.; Barbee, R.W.; Reynolds, P.S.; Torres, I.P.; Tiba, M.H.; Torres, L.; Pittman, R.N.; Terner, J., Oxygenation monitoring of tissue vasculature by resonance Raman spectroscopy. Analytical Chemistry 2007, 79, 1514-1518.
Kuhnel, K.; Derat, E.; Terner, J.; Shaik, S.; Schlichting, I., Structure and quantum chemical characterization of chloroperoxidase compound 0, a common reaction intermediate of diverse heme enzymes. Proceedings of the National Academy of Sciences of the USA 2007, 104, 99-104.
K. R. Ward, R. W. Barbee, J. Terner, R. R. Ivatrury, F. M. Hawkridge, US Patent 7,113,814 B2, “Tissue Interrogation Spectroscopy,” September 2006.