Modelización del aprendizaje en valoración contingente Carmelo J. León; Francisco J. Vázquez Polo
Investigaciones económicas,
2000, Letnik:
Investigaciones Económicas (España) Num.001 Vol.XXIV, Številka:
1
Journal Article
Protein‐deficient ribosomal particles obtained by treatment of 50‐S subunits from Escherichia coli ribosomes with I M NH4Cl and 50% ethanol contain less than 3 % of proteins L7 and L12 and about 7 % ...of proteins L10 and L11. Proteins L1, L5, L8/9 and L25 are also released during the treatment but in amounts accounting for less than 40%.
The particles are able to form peptide bonds in different systems, such as ‘fragment reaction’, puromycin reaction and formation of dipeptides. They also bind N‐acetylphenylalanyl‐tRNA and phenylalanyl‐tRNA non‐enzymically but are unable to support any of the elongation‐factordependent reactions tested. However, when methanol is present, they display up to 20% of the control EF‐G‐dependent GTP activities, such as GTP hydrolysis and formation of the ternary complex EF‐G. GuoPP(CH2)P · ribosome. The first activity is totally sensitive to the antibiotic thiostrepton while the formation of the ternary complex is unaffected by the drug. When measured by equilibrium dialysis the core particles are shown to be able to bind radioactive thiostrepton.
The results show that protein L11 is not an absolute requirement either for peptidyl transferase activity or for the binding of thiostrepton, although in the last case the protein strongly enhances the ribosome affinity for the antibiotic.
Protein‐deficient ribosomal particles obtained by treatment of 50‐S subunits from Escherichia coli ribosomes with I M NH
4
Cl and 50% ethanol contain less than 3 % of proteins L7 and L12 and about 7 ...% of proteins L10 and L11. Proteins L1, L5, L8/9 and L25 are also released during the treatment but in amounts accounting for less than 40%.
The particles are able to form peptide bonds in different systems, such as ‘fragment reaction’, puromycin reaction and formation of dipeptides. They also bind N‐acetylphenylalanyl‐tRNA and phenylalanyl‐tRNA non‐enzymically but are unable to support any of the elongation‐factordependent reactions tested. However, when methanol is present, they display up to 20% of the control EF‐G‐dependent GTP activities, such as GTP hydrolysis and formation of the ternary complex EF‐G. GuoPP(CH
2
)P · ribosome. The first activity is totally sensitive to the antibiotic thiostrepton while the formation of the ternary complex is unaffected by the drug. When measured by equilibrium dialysis the core particles are shown to be able to bind radioactive thiostrepton.
The results show that protein L11 is not an absolute requirement either for peptidyl transferase activity or for the binding of thiostrepton, although in the last case the protein strongly enhances the ribosome affinity for the antibiotic.
70‐S ribosomes and 50‐S ribosomal subunits from Escherichia coli D10 were treated with proteinase K for increasing periods of time. Peptidyl transferase activity and sparsomycin‐induced binding of ...(U)C‐A‐C‐C‐A‐3HLeu‐Ac were tested in the treated particles, the binding of the substrate being more sensitive to the protease than peptide bond formation. Comparison of the amounts of proteins present in the treated particles with the residual activity indicates that only proteins L3 and L14 are released at a similar rate to that at which peptidyl transferase activity is lost. Proteins related to this ribosomal activity by other techniques are lost at a faster rate than the activity itself. In addition, the results indicate that sparsomycin stimulates the binding of the substrate by a different mechanism from that which inhibits peptide bond formation.
Radioactive ribosomes from Escherichia coli were treated with increasing concentrations of NH4Cl in the presence of 50 % ethanol. The resulting particles were tested for peptidyl transferase activity ...as well as for the binding of (U)C‐A‐C‐C‐A‐Leu‐Ac, (U)C‐A‐C‐C‐A‐Leu, chloramphenicol, lincomycin and erythromycin. At the same time the proteins present in the particles were quantitatively estimated and the amount of each related to the residual activity displayed by the treated ribosomes. It was found that the loss of protein L 16 closely paralleled the inactivation of the particles implying an important role for this protein in the structure of the peptidyl transferase center.
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