The cell-free E. coli system worked out by Matthaei & Nirenberg (1961) improved markedly the incorporation of radioactive amino acids, as compared to the method with liver cells. Cell extracts could be obtained in large, workable amounts and freezed in smaller portions, so that comparable conditions could be granted for many experiments. The system was so convenient that it incited even further optimization, as it was still far from ideal; a real, biochemically measurable net synthesis of protein mass, for instance, was not attainable The rate of protein synthesis was minimal. There were only traces of newly synthesized proteins and these could only be detected through their radioactivity. A significant improvement consisted in pre-incubating the cell homogenate with DNAase, a measure which brought the inherent background incorporation of the system to an almost complete halt after roughly 20 min. Thus, the effect of specific substances added to the system could be more clearly detected.
KeywordsSynonym Codon Amino Acid Site Polypeptide Synthesis Radioactive Amino Acid Amina Acid
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