Conformational studies of nadph cytochrome P-450 reductase by circular dichroism: Interaction with phospholipids

Abstract 1. 1. Ultraviolet circular dichroism spectrum of purified NADPH cytochrome P -450 reductase was characterized by two negative bands centered at 208 and 222 nm. The approximation of the α-helical content from the value of the mean residue ellipticity at 222 nm indicated 28% of α-helical structures. 2. 2. Heat inactivation of the enzyme was associated to a drastic change in the secondary structure of the protein. 3. 3. Membrane reconstitution experiments by inclusion of the enzyme into liposomes revealed that the conformation of NADPH cytochrome P -450 reductase was sensitive to its phospholipid environment. Egg lecithin as well as synthetic phosphatidylcholines, at the optimal phospholipid-enzyme molar ratio 200, was able to increase up to 37% the mean residue ellipticity at 222 nm. Addition of phosphatidylserine or phosphatidylethanolamine produced no effect. 4. 4. Non-ionic detergent such as Emulgen 913 weakly enhanced the mean residue ellipticity.