Isolation and characterization of ribonucleoprotein particles from heart muscle

Preparation and some properties of rat skeletal-muscle polyribosomes

1. A method is described for the sucrose-gradient sedimentation analysis of ribosomes in a post-mitochondrial supernatant of rat skeletal muscle. 2. An essential feature of the method involves the use of buffer of ionic strength 0.3 for homogenization of the muscle tissue. 3. Polyribosomes can be prepared by precipitation from post-mitochondrial supernatant of skeletal muscle by adjustment of the potassium chloride content of the medium. These polyribosomes stimulate cell-free amino acid incorporation in vitro in an energy-dependent system. 4. Ribosome aggregates of uniform size distribution can be obtained by adjustment of the ionic strength of the post-mitochondrial supernatant, followed by differential sucrose-gradient centrifugation. 5. In vivo, rat skeletal-muscle polyribosomes became labelled by (14)C-labelled amino acid within 15min., and radioactivity was associated with the light ribosome species within 45min. 6. Electron microscopy of the polyribosomes revealed aggregations containing more than 40 single ribosomes.

Mammalian ribosomal protein: analysis by electrophoresis on polyacrylamide gel

Ribosomal protein from five mammalian tissues when analyzed by discontinuous electrophoresis on polyacrylamide gel at pH 4.5 yielded 24 bands. Densitometric tracings indicated that the patterns of the basic ribosomal proteins from the several tissues were qualitatively similar. Protein from Escherichia coli ribosomes analyzed at pH 4.5 gave 29 bands, and the pattern was different from that of mammalian ribosomal protein. No distinct band was found when mammalian ribosomal protein was analyzed at pH 8.3 (acidic proteins). Ribosomal protein from Escherichia coli gave eight bands at pH 8.3. Thus, the structure of the genes responsible for synthesis of ribosomal protein in several mammalian tissues is the same, and different genes direct synthesis of ribosomal protein in bacteria.

Protein synthesis by heart muscle ribosomes: an effect of insulin independent of substrate transport

Ribosomes from heart muscle of diabetic animals perfused for 15 minutes with insulin, but without added substrate, were more active in the catalysis of protein synthesis than were ribosomes from hearts perfused without insulin. This effect of insulin on the efficiency of protein synthesis seems not to result from transport of some critical substrate into muscle, nor is the effect on ribosomes mediated by a product of a tissue other than muscle.

Protein synthesis by ribosomes from heart muscle: effect of insulin and diabetes

Incorporation of phenylalanine into protein by ribosomes from the heart muscle of rats is decreased when the ribosomes are from alloxan-diabetic animals. Protein synthesis is increased when the ribosomes are obtained from nondiabetic animals I hour after treatment with insulin. The change due to insulin appears to be an alteration in the function of the ribosome.