Protein synthesis in resting and stimulated human lymphocytes

Summary The ribosomal profiles in lysates from resting and phytohemagglutinin stimulated human lymphocytes have been analyzed by sucrose gradient centrifugation. The percentage of polyribosomes increased during lymphocyte transformation reaching a maximal value of 60 to 70% of the total ribosomes after 72 hours of mitogen addition. This time period coincides with maximalin vivo protein synthesis. On the other hand, in nonstimulated lymphocytes, about 25% of the ribosomal particles appeared as aggregates, independently of the incubation period.Experiments performed with homologous cell free systems containing ribosomes and supernatant fluids prepared from unstimulated or activated lymphocytes demonstrate that the mixtures containing both components from stimulated lymphocytes are several fold more active in polypeptide synthesis than the systems which contain ribosomal particles and cell sap from resting cells. Assays carried out with mixtures combining the components from both sources indicate that the increased activity depends on ribosomes as well as on the supernatant fractions.Dedicated to Professor LUIS F. LELOIR on the occasion of his 70^th birthday.