Interaction of Hydrophobic Molecules with Heme Proteins

We have been measuring the Km and Vmax parameters of cytochrome oxidase in intact mitochondria in the presence and absence of lidocaine, tetracaine, and procaine anesthetics. Data suggests that cytochrome oxidase is not as sensitive to these compounds as is succinate oxidation. Early findings in intact mitochondria indicate that tetracaine and procaine, but not dibucaine or lidocaine, cause shifts in the 604 nm alpha band of cytochrome oxidase. Also, dibucaine, tetracaine, and lodocaine cause 20-30 mV increases in apparent midpotential of the oxidase in mitochondria. We have not yet studied isolated oxidase. We have done two types of experiments on myoglobin. The first investigates changes in the protein by anesthetics. Thus far, procaine, tetracaine, and dibucaine have not caused noticeable changes at 5 mM concentration. Lidocaine, however, causes a significant change in the 3.7 ppm resonance. The second type of experiment assays changes in the anesthetic due to interaction with myoglogin. No changes were observed with procaine, but dramatic changes were observed with lidocaine with less prominent changes in dibucaine and tetracaine. Cytochrome c has resonances at g3 and g2.2 that we are studying. No compound alters the position of g2.2, but all narrowed the half-bandwidth narrowed the signal without an increase in peak height in other words, a change in microwave extinction coefficient is not observed.