In vivo and in vitro function of the intracellular proteolytic apparatus in nongrowing Bacillus megaterium under heat stress

In Bacillus megaterium sporulating at 35 degrees C, up to 90% of 10-min pul se-labeled proteins were degraded. Degradation proceeded in two waves. Shor t-lived proteins, i.e., intrinsically labile proteins and proteins made sho rt-lived because of starvation, were mostly degraded during the reversible sporulation phase. Their amount corresponded to 20% or slightly more during 2 h, The second wave of protein degradation, which followed during the irr eversible sporulation phase at 35 degrees C, increased the amount of total degradable pulse-labeled proteins to about 90%. This wave was absent in the isogenic asporogenic mutant 27-36 or in the wild strain, whose sporulation was inhibited by increased temperature. The proportion of degradable prote ins was thus reduced to less than 40% in the asporogenic mutant incubated a t 35 degrees C and to 46% in the wild strain whose sporulation was suppress ed by the temperature of 47 degrees C, Unlike sporulating cells, these cell s were thus capable of degrading short-lived and denatured proteins, but we re not able to degrade most of other proteins. The in vitro protein degrada tion was substantially enhanced by increasing the Ca2+ concentration, sugge sting a role of Ca2+-dependent proteinase(s) in the process.