Effects of heat and amino acid supplementation on the uptake of arginine and its incorporation into proteins in Eschericia coli

Hyperthermic treatment reduces protein synthesis and modifies amino acid transport in Escherichia coli. The present study examined the role of nutrient availability on these processes. Cultures of E. coli in log phase were aliquoted into growth medium with or without complete amino acid supplementation and exposed to 37, 44, or 48°C for 10 min. Amino acid supplementation increased radiolabelled arginine uptake at 48°C when compared with unsupplemented cells. Exposure to 48°C also reduced protein synthesis in both groups by at least 50% as reflected by labelled arginine incorporation. Two-dimensional gel electrophoresis indicated that this heat-related decrement in synthesis was most apparent in basic proteins. Total density analysis of the fluorographs demonstrated reductions in basic proteins of 15% at 44°C and 89% at 48°C, while acidic proteins only showed an 80% reduction at 48°C. Amino acid supplementation appears to raise the baseline, but not to modify the final results of hyperthermia-induced inhibition of protein synthesis. The sensitivity of basic protein synthesis seems to be a key event in this process.