Subcellular localization of acid proteinase in barley mesophyll protoplasts.

Chloroplasts prepared from lysed protoplasts of barley mesophyll contain 2-8% of the total acid proteinase activity. This residual activity is not associated with intact chloroplasts isolated by means of density gradient centrifugation. Vacuoles isolated from lysed protoplasts contain 80-85% of the total acid proteinase activity, indicating that the enzyme(s) which is presumably responsible for the degradation of chloroplastic proteins is located largely in the central vacuoles of mesophyll cells.