AMINO ACID INCORPORATION BY ISOLATED CHLOROPLASTS

1. 1. Characteristics of amino acid incorporation by chloroplasts, isolated in a Honda medium from leaves of several higher plants, were compared. The effect of Mg concentration in the isolation medium varied depending on the plant, but other characteristics were similar. Chloroplasts from younger leaves were more active, but no sign of a diffusible inhibitor was found in older leaves. 2. 2. Chloroplast activity was very sensitive to physical disruption, such as by freezing and thawing, by aging in a hypotonic medium or by centrifuging and resuspending. Perhaps a significant part of the ribosomes were bound to chloroplast lamellae and could not be easily liberated by hypotonic extraction, but these might be detachable in the reaction medium after incubation. Radioactive amino acids were found to be associated with tRNA, with ribosomes probably in the form of nascent peptides, and finally with the photophosphorylation coupling factor after purification. © 1969.