Dependence of spectral and structural properties of resting cytochrome oxidase on temperature.

The temperature effect on isolated resting oxidized oxidase was investigated by optical and EPR spectroscopy. The reversible decrease of the optical alpha-band absorption is linear with temperature increase from 5 to 30 degrees C. The temperature increase also causes an irreversible change of the suspension turbidity and the Arrhenius plot of mobility of lipid-soluble spin labels is nonlinear. A significant enhancement of turbidity is observed on heating from 30 to 50 degrees C, with an apparent transition temperature at 43 degrees C. The change of turbidity and the nonlinear behaviour of spin label mobility are being ascribed to denaturation of non-heam-containing subunits followed by an aggregation of the enzyme.