Electrophoretic studies on proteins and ribonucleic acids of free and membrane-bound ribosomes

Analysis by two-dimensional polyacrylamide gel electrophoresis of liver ribosomal subunnit proteins obtained from free and membrane-bound polysomes of unfasted animals

Ribosomal proteins were analyzed by means of two-dimensional gel electrophoresis. To insure that the analysis included only that fraction of the ribosome actively participating in protein synthesis, only polysomal-bound ribosomes were used. This differs from previously reported analyses of liver ribosomal proteins. The ribosomal proteins were prepared from ribosomes of polysomal origin from membrane-bound and free polysomes. Membrane-bound and free liver polysomes were isolated from unfasted mice. The polysomes were purified on hydroxyapatite under conditions known to result in polysomes and ribosomes that are active in both endogenous and synthetic mRNA translation. Moreover, this is the first time that liver ribosomal protein was obtained and analyzed from animals that have not been starved prior to sacrifice. The puromycin-released ribosomes were dissociated into subunits and ribosomal proteins were analyzed by means of two-dimensional polyacrylamide gel electrophoresis. When 100-200 mug samples of the ribosomal subunit proteins were analyzed by two-dimensional electrophoresis, approximately 32 major proteins were detected for the 60 S ribosomal subunit and 25 major proteins for the 40 S ribosomal subunit. A total of 13 "fractional" ribosomal proteins was also detected in the ribosomal subunit profiles. No differences in number or mobility of the ribosomal proteins were found between the membrane-bound and free ribosome populations. We describe a system in which all ribosomal proteins are completely solubilized and quantitatively move from the first to the second dimension gel. Thus the total sample is separated and fractionated. This procedure elimates artifacts due to incomplete solubilization of ribosomal proteins, which is common for the transfer from the first- to second-dimension gel. Therefore, a more detailed and accurate analysis is achieved.

The pyruvate-dehydrogenase complex from Azotobacter vinelandii. 2. Regulation of the activity

The presence of activators(AMP and sulphate) or inhibitors(acetyl-CoA) has no influence on the Hill coefficient of the S-shaped [pyruvate]--velocity curve of either the pyruvate-NAD+ overall reaction(h equals 2.5) or that of the pyruvate-K3Fe(CN)6 ACTIVITY OF THE FIRST ENZYME (H EQUALs 1.3). pH STUDIES INDICATED THAT THE Hill coefficient is dependent on subunit ionization within the pyruvate-containing complex and not on those in the free complex. It is concluded that pyruvate conversion rather that pyruvate binding is responsible for the allosteric pattern. The activity is due to absence of a protein kinase, mainly regulated at the acetyl-CoA/CoA, and NADH/NAD+ levels and by the value of the energy charge.

Protein synthesis by membrane-bound and free ribosomes of secretory and non-secretory tissues

1. Methods for the separation of membrane-bound and free ribosomes from rat brain (cortex) and skeletal muscle were described and the preparations characterized by chemical analysis and electron microscopy. The attachment of ribosomes to membranes is not an artifact of the separation procedure. 2. The rate of incorporation of l-[(14)C]leucine into protein in vitro by the membrane-bound and free ribosomes from these two predominantly non-protein-secreting tissues is compared with that by similar preparations from rat liver. With all three tissues the initial rate was higher for the membrane-bound preparations. 3. By using the technique of discharging nascent polypeptide chains by incubation with puromycin followed by treatment with sodium deoxycholate (Redman & Sabatini, 1966), a major difference was observed for the vectorial discharge of nascent protein synthesized both in vivo and in vitro on membrane-bound ribosomes from liver, on the one hand, and brain and muscle, on the other. Whereas a large part of nascent protein synthesized on membrane-bound liver ribosomes was discharged into the membranous vesicles (presumably destined for export from the cell), almost all nascent protein from membrane-bound ribosomes from brain and muscle was released directly into the supernatant. Incorporation of [(3)H]puromycin into peptidyl-[(3)H]puromycin confirmed these findings. There was thus no difference between membrane-bound and free ribosomes from brain on the one hand, and from free polyribosomes from liver on the other, as far as the vectorial release of newly synthesized protein was concerned. 4. Incubation with puromycin also showed that the nascent chains, pre-formed in vivo and in vitro, are not involved in the attachment of ribosomes to membranes of the endoplasmic reticulum. 5. The differences in vectorial discharge from membrane-bound ribosomes from liver as compared with brain and muscle are not due to the different types of messenger RNA in the different tissues. Polyphenylalanine synthesized on incubation with polyuridylic acid was handled in the same way as polypeptides synthesized with endogenous messenger. 6. It is concluded that there is a major difference in the attachment of ribosomes to the membranes of the endoplasmic reticulum of secretory and non-secretory tissues, which results in a tissue-specific difference in the vectorial discharge of nascent proteins.

Development of the metanephric kidney. Protein and nucleic acid synthesis

The metanephric kidney was studied in fetal and older mice beginning at 16 days after mating of the parents. Polyribosomes from fetal kidneys labeled in vitro with 14C-labeled amino acids had 10-20 times more acid-precipitable radioactivity associated with them than polysomes from adult kidneys similarly labeled. Between 3 and 6 days after birth the rate incorporation of labeled amino acids by polyribosomes from neonatal kidneys declined sharply to only twice the value found for adult kidneys. There was no change in the shape of the polyribosome profile with increasing age, but before birth few, if any, ribosomes were bound to membranes compared with 20% 2 days after birth and between 20 and 30% in the adult. Total protein represented less than 10% of the wet weight in the fetal kidney but increased to 17% of the wet weight in the adult kidney. There was a steady decline in the concentration of RNA and DNA with respect to dry weight throughout kidney development. DNA concentration declined more rapidly than RNA concentration, so that the milligram to milligram ratio of RNA to DNA increased. In males the RNA/DNA ratio was stable at 1.3 at 40 days after birth; but in females the decline in DNA concentration was more protracted, and at 200 days after birth the RNA/DNA ratio was only 0.99. Thus, total nucleic acids show only gradual changes in concentration throughout development of the kidney, but a sharp change in the synthetic activity of the ribosomes and in their binding to membranes occurs in kidneys soon after birth.

The formation and distribution of ribosomes during hormone-induced growth and development

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