RESUMO
The inactivation temperature for Hill activity and for the long-lived delayed fluorescence of isolated Pisum sativum L. chloroplasts was found to depend on pH, the maximal value being in the pH region 5-7. Salts increase the inactivation temperature by 4-7°C. Effects of D2O and some other substances that modify the thermostability of chloroplasts are dependent on pH. It is concluded that thermal denaturation of proteins is the most probable mechanism for heat inactivation of chloroplasts.
RESUMO
Unsaturated fatty acids at concentrations of 1-2 µmol mg(-1) chlorophyll decrease the intensity of long-lived delayed fluorescence and inhibit the Hill reaction in Pisum sativum L. chloroplasts in a pH-dependent and reversible manner. A charged form of the fatty acids is two times more effective than an undissociated form. Fatty acids, anionic and cationic detergents and urea inhibit activity and decrease the temperature of heat inactivation of the water-spilitting system. Sucrose at a concentration of 2.5 M protects chloroplasts against the effects of these compounds. It is concluded that their action can be explained by the denaturation of the water-splitting protein.
