SYNTHESIS OF MYOGLOBIN BY MUSCLE POLYSOMES

1. Polysome preparations derived from muscle, but not from liver, of the duck brought about incorporation of uniformly 14C-labeled lysine into antibody-detectable myoglobin in vitro. This synthesis of myoglobin accounted for approximately 5-9% of the total soluble protein synthesis demonstrable in this system. 2. Tetrameric, pentameric and hexameric polysomes seemed to be the active components in myoglobin synthesis. 3. The efficiency of myoglobin synthesis per unit of polysomes in the standard cell-free system was the same in preparations obtained from immature and adult ducks, although approx. 8 times as much polysomal material could be isolated from immature muscle. 4. Myoglobin (0.06-0.08 mM) produced slight, though consistent, stimulation of myoglobin synthesis. Concentrations of myoglobin above 0.15 mM inhibited myoglobin synthesis in vitro. There was no detectable effect of these concentrations of added myoglobin on total protein synthesis measured as a whole, however. 5. The combination of reduced polysome content, and reduced efficiency may account for the reduced synthetic ability of adult muscle, for myoglobin, compared to immature muscle. © 1969.