Protein synthesis by attached pulmonary macrophages. Effect of phagocytosis

We studied the effect of phagocytosis of polystyrene latex beads on protein synthesis by pulmonary macrophages. To do this we determine the specific radioactivity of extracellular and intracellular free phenylalanine and of phenylalanine released from tRNA and used this information in calculating the rates of protein synthesis. Phagocytosis resulted in an increased rate of protein synthesis irrespective of which precursor specific radioactivity was used in the calculation. The rate of protein synthesis was increased per microgram polyribosomal RNA; but there was no increase in the amount of polyribosomal RNA in phagocytizing macrophages. The increase in the rate of protein synthesis (1.4-fold) was almost identical to the increase (1.3-fold) in the rate of ribosome transit in phagocytizing compared to nonphagocytizing macrophages. The decreased ribosome transit time during phagocytosis occurred without a fall in the average molecular weight of macrophage proteins. We conclude that phagocytosis increases the rate of protein synthesis in attached pulmonary macrophages and that this increased rate of synthesis can be accounted for almost completely by an increased rate of polypeptide chain elongation and/or termination.