[Kinetics and mechanism of inactivation of isolated chloroplasts]

A detailed kinetic analysis has been performed of a multistep inactivation of chloroplasts. The kinetic model suggested involves the formation of chloroplast forms differing in stability and activity. A comparison of the kinetic model with the experimental data shows that the mechanism of inactivation of isolated pea chloroplasts consists of at least two forms displaying different activity in the Hill reaction and different stability in solution. The effect was studied of the nature of the buffer and destruction products on the kinetics of chloroplast inactivation in the process of "ageing". In phosphate buffer, where the concentration of phosphate exceeds 40 mM, the effect of the destruction products of chloroplasts on their inactivation is insignificant. The pH dependence on the inactivation kinetics suggests that the pH region from 6 to 9 affects only the rapid kinetic process resulting in the increase in the chloroplast activity; irreversible inactivation of chloroplasts is pH-independent. The temperature dependence of the irreversible inactivation kinetics has been studied and the activation parametres of this stage have been determined. Possible molecular mechanism of the limiting stages of the inactivation of isolated chloroplasts are discussed, which can explain the kinetic data obtained.