Proteins newly formed from labeled amino acids by isolated intact pea chloroplasts are not entirely stable. Between 20 and 35% of the labeled protein is degraded over a 20–30 min incubation period in pulse-chase experiments. Protein degration is prevented when chloroplast ATP level drops, as in the dark without added ATP. Degration is stimulated by adding ATP directly or by generating it in photophosphorylation. Susceptible new proteins are not stabilized against further additions of ATP, during incubation under ATP-deficient conditions.
