SOLUBILIZATION AND HETEROGENEOUS NATURE OF PROTEINS FROM RIBOSOMES OF PEA-SEEDLING BUDS

Abstract

The results of several procedures for solubilizing protein from pea-seedling ribosomes are described. Pancreatic ribonuclease (RNAase), alone at pH 8.0 and low ionic strength, solubilized 10%, whereas subsequent treatment with dilute HC1 solubilized a further 29%. RNAase in 8 M urea at pH 5.5 solubilized more than 90% of the ribosomal protein. After removal of ribonucleic acid fragments, all of this material, termed "total protein", remained in solution in 0.05 M acetate buffer at pH 5. Proteins solubilized by these three procedures were subjected to electrophoresis on starch–urea gels, amino acid analyses, and fingerprinting after digestion with trypsin and chymotrypsin. The protein soluble in RNAase probably contains only one or two components and is distinct in amino acid and peptide composition from the remainder of the ribosomal protein. Protein soluble in HC1 is representative of much of the "total protein" and both HC1-soluble and "total protein" are complex. Fingerprints showed that although RNAase-extracted protein and three fractions of "total protein" obtained by gel electrophoresis were different, they also possessed a number of peptides in common. It was concluded that the number of components in pea-ribosomal proteins is probably of the order of 16, the number of bands seen in gel-electrophoretic patterns.