PHYSICOCHEMICAL CHEMICAL AND BIOLOGICAL STUDIES ON WHEAT EMBRYO RIBOSOMES

Wheat embryo ribosomes with a nucleic acid protein content of 55 and 45%, respectively, have been isolated and subjected to a detailed physic ochemical investigation using the techniques of sedimentation velocity, diffusion, viscometry, pycnometry, ultraviolet absorption, and optical rotatory dispersion. The intrinsic sedimentation constant, determined by both schlieren and ultraviolet optics, is 80 S and the D020,w value, evaluated through the use of the Moller method, is 1.15 x 10-7 cm2/sec. The molecular weight of the particle was estimated from the Svedberg equation as 4.25 ([plus or minus] 0.5) x 106, and it contains approximately 80% of its enclosed volume as water of hydration. Three ultracentrifugally identifiable components with s0 20,w values of 60, 40, and 26 S, respectively, are obtained as dissociation products when magnesium is removed from the ribosomes, and in this respect this system behaves similarly to ribosomes from other plant sources. Optical rotatory dispersion studies on wheat embryo ribosomes and their constitutent ribonucleic acid (RNA) and proteins indicate that the ribosomal proteins are similar to protamines in that they have little [alpha]-helical content, and that the conformation of RNA and proteins inside the ribosome is very similar to that in the free state. In agreement with reports by other workers, an amino acid incorporating system may be obtained from wheat embryos. This system has very low endogenous activity, but phenylalanine incorporation can be stimulated by the addition of polyuridylate.