Thermolability of protein synthesis in a cell-free system from the obligately psychrophilic yeast Candida gelida

Abstract

A subcellular amino-acid-incorporating system from the obligately psychrophilic yeast, Candida gelida, was completely inhibited after incubation at 35 C for 30 minutes. The thermal inactivation of protein synthesis was due, in part, to the presence of unusually temperature-sensitive aminoacyl-sRNA synthetases in C. gelida extracts. Of the 13 specific synthetases examined, 7 retained less than 50% of their activity after being held at 35 C for 30 minutes. Kinetic studies of thermal inactivation of leucyl-sRNA synthetase demonstrated that this enzyme is 50% inactivated after only 7 minutes at 35 C. None of the 10 sRNA species tested was temperature sensitive. In addition to temperature-sensitive synthetases, C. gelida possesses thermolabile soluble enzymes involved in the formation of ribosomal-bound polypeptide chains.