In the psychrophilic bacterium sp. strain ANT-300, the rate of protein degradation , measured at fixed temperatures, increased with elevation of the growth temperature. A shift in growth temperature induced a marked increase in this rate. Dialysed cell-free extracts hydrolysed exogenous insulin, globin and casein (in decreasing order of activity) but did not hydrolyse exogenous cytochrome Cells contained at least seven proteases separated by DEAE-Sephacel chromatography, one of which was an ATP-dependent serine protease. The ATP-dependent proteolytic activity in extracts of cells incubated for 3 h at 16 °C after a shift-up from 0 °C increased to a level 36% and 17% higher than that of cells grown at 0 °C and 13 °C, respectively. A shift-down to 0 °C from 13 °C induced only a slight increase in the proteolytic activity. Extracts of all cells, whether exposed to temperature shifts or not, showed the same temperature dependence with respect to both ATP-dependent and ATP-independent protease activity. In all the extracts these proteases also exhibited the same heat lability. The ATP-dependent protease was inactivated by incubation at temperatures above 25 °C. There was an increase in ATP-independent protease activity during incubation at temperatures between 25 and 30 °C, but a decrease at 35 °C and higher. These results suggest that the marked increases in proteolysis , caused by a shift in temperature, may result not only from increases in levels of ATP-dependent serine protease(s) but also from increases in the susceptibility of proteins to degradation.


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