Differences in the Regulation of the Intracellular Ca²⁺-Dependent Serine Proteinase Activity Between Bacillus subtilis and B. megaterium

Abstract

A rise of the intracellular serine proteinase activity (ISP) during postexponential growth of Bacillus subtilis was decreased by a temperature upshift from 35° to 42°C. However, the amount of both molecular forms of the major intracellular serine proteinase ISP1 determined by immunoblotting was similar at both temperatures or even slightly increased at 42°C. The evolution of the ISP activity in B. megaterium showed an opposite temperature dependence, being faster during growth at 42°C. The amount of immunologically detected ISP1 again did not correlate well with the enzyme activity. Moreover, most of the ISP1 molecules in cell-free extracts from B. megaterium were inactive and were activated by increasing the CaCl₂ concentration up to 30 mm—unlike B. subtilis, where the enzymic activity was unaffected by Ca²⁺ concentration. These data suggest that the ISP1 activity in the two bacillar species during postexponential growth is regulated posttranscriptionally, but that the regulatory mechanisms differ.