The molecular basis of the selectivity of protein degradation in stressed senescent barley (Hordeum vulgare cv. Proctor) leaves.

The molecular basis for the selectivity of protein degradation has been examined in osmotically stressed and senescent barley leaves. Relatively weak correlations between the in-vivo rate of loss of enzyme activity, and the charge and molecular weight of the enzymes ahve been detected. We interpret these correlations as supporting the view that the selectivity of enzyme degradation is the result of the physical properties of the enzymes being degraded. The weakness of the correlates is taken to mean that a number of properties which contribute to the selectivity are independent of one another. Under in-vitro conditions (autolysis at 0° C), the loss of enzyme activity was weakly correlated with the charge of the enzymes. However, there was a general similarity between the in-vivo pattern of loss of enzyme activity and the in-vitro patterns under a number of conditions. Furthermore double-isotope experiments demonstrated that the in-vivo degradation of soluble protein was reflected by in-vitro degradation under a number of conditions. Consequently we conclude that the selectivity of protein degradation is largely independent of the nature of the proteolytic system.