SUMMARY: Proteolytic activities, active against casein and insulin are present in cell-free extracts of the psychrotrophic bacterium S55. These activities were compared (i) following growth of the bacterium at different temperatures (10, 20 and 32°C) and (ii) after a temperature shift from 10 to 32°C. Both activities (measured at 20°C) were greater in cells grown at 32°C and after a temperature shift. Chloramphenicol prevented the increases in activities. The proteolysis of casein was stimulated by ATP; the stimulation was greater following a temperature shift. In addition, proteolysis of casein (measured at 20°C) was activated by pre-incubation at temperatures between 45 and 60°C; the proportion of proteolytic activity activated by such treatment also increased with growth temperature. Comparison by two-dimensional electrophoresis of the polypeptides synthesized at 10 and 32°C suggests that S55 produces proteins specific to both temperatures (13 species were either exclusive to or present in increased amounts during growth at 10°C, while at least 21 polypeptides were preferentially synthesized at 32°C). A temperature shift from 10 to 32°C promoted the synthesis of at least 16 polypeptides, many with values similar to those of heat shock proteins synthesized at higher temperatures in mesophiles. A temperature up-shift of S55 from 10 to 20°C did not provoke the synthesis of new proteins; heat shock proteins were produced only at 28°C and higher. The similarity in kinetics of the appearance of heat shock proteins and the increase in proteolytic activities suggest that in S55 some heat shock proteins might also possess protein catabolic function.


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