Extraction and comparison of bean cytoplasmic and chloroplast ribosomes

1. In isolation of total ribosomes from Phaseolus leaves the highest yield was obtained with an extraction medium containing HEPES buffer, low Mg2+-concentration (1 mM) and SH-group protecting agents. 2. Chloroplast and cytoplasmic ribosomes were obtained in a ratio of 1 : 28 after selective isolation. 3. After freezing identical portions of cytoplasmic extract the amount of ribosomes/ml extract dropped, but later increased with freezing time. 4. Ribosomal preparations showed UV-absorption spectra typical for RNA. Extinction ratios suggested that preparations were contaminated with extraneous protein to a certain extent, purity increasing after selective isolation, especially after freezing. 5. Protein patterns and sedimentation behaviour of cytoplasmic ribosomes were identical regardless of addition or omission of detergent in leaf exeracts. 6. After polyacrylamide gel electrophoresis of ribosomal proteins, 29 bands of basic protein were found in cytoplasmic ribosomes and 22 in chloroplast ribosomes. Acidic proteins could not be detected. Patterns in both extracts were different and highly reproducible, resembling those recently reported. Tests for five enzymes, highly active in the leaf tissue, gave negative results on the isolated ribosomal proteins.