Rats were exposed to 150 J (600 pulses of 0.25 J at 1-sec intervals) of CO2 laser irradiation (10,600 nm) 2 days prior to removing the liver and measuring protein synthesis in liver homogenate fractions. The incorporation of <tex-math>$[{}^{14}{\rm C}]\text{phenylalanyl-}{\rm tRNA}$</tex-math> into peptide was increased when salt-washed control liver ribosomes were incubated with the pH 5 supernatant fraction obtained from the irradiated liver. Chartreusin, an antibiotic which inhibits elongation factor 1-dependent binding of aminoacyl-tRNA to ribosomes, caused a lower inhibition of peptide synthesis when the pH 5 supernatant fraction of irradiated liver was used than when the pH 5 supernatant fraction of control liver was used. Purification of elongation factor 1 and elongation factor 2 by gel filtration and chromatography showed that the activity of elongation factor 1, but not that of elongation factor 2, was increased in the laser preparations.

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