Amino acid-activating systems from pig liver

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Abstract
Extracts of pig liver contain 50% of the soluble protein and 15-20% of the particulate material released by homogenizing the tissue by orthodox methods. The particulate material can be removed by treatment of the extract with protamine sulfate, followed by centrifuging at relatively low speeds. Precipitation of the protamine-treated extract with ammonium sulfate and potassium acetate yields a protein fraction which will catalyze the activation of several amino acids, as measured by exchange of [P32]pyrophosphate, to an extent very similar to that observed with pH 5.0 fractions prepared from the extract. This protein fraction is very low in ribonucleic acid (RNA) and is non-precipitable at pH 5.0 unless RNA is added. The material with little RNA readily catalyzes the incorporation of [C14] amino acids into added isolated "soluble" RNA obtained from either pig or rat liver.