Heat-labile Enzymes in a Psychrophilic Bacterium

The oxidative and fermentative activities of a psychrophilic bacterium (strain 82), whose maximal growth temperature is 35 C, were completely destroyed by exposure of the cells to 46 C for about 1 hr, whereas those of mesophilic Escherichia coli were unaffected. Similar results were obtained with cell-free extracts. In attempts to determine some of the specific enzymes inactivated in strain 82 by exposure to 46 C, it was found that reduced nicotinamide adenine dinucleotide oxidase was completely inactivated at 46 C in 2 hr. Also, cytochrome c reductase was completely destroyed at 46 C in 1 hr and was 70% destroyed at 40 C in 2 hr. The heat lability of the latter may determine the maximal growth temperature of the organism. In addition, the results indicated that the enzymes of strain 82 involved in the clastic split of pyruvate to formate and acetate are inactivated by exposure to 46 C and that the lactic and glycerol dehydrogenases are more heat-labile than those in E. coli. Succinic, nicotinamide adenine dinucleotide phosphate-alcohol, and glucose-6-phosphate dehydrogenases, however, in both strain 82 and E. coli, were essentially unaffected by exposure to 46 C for 2 hr.