Changes in enzyme stability and fatty acid composition of Streptomyces sp., a facultative thermophilic actinomycete.

The thermostability of several enzymes from the facultative thermophilic actinomycete Streptomyces sp., derived from cells grown in the temperature range from 37 degrees C to 60 degrees C, has been examined. A correlation between the growth temperature of the cultures and the heat stability of the enzymes could be demonstrated for alanine dehydrogenase, isocitrate dehydrogenase, myokinase and pyruvate kinase. Except for the isocitrate dehydrogenase, which showed a linear increase of its stability throughout the entire temperature range, all enzymes exhibited a steep increase of the heat stability up to about 50 degrees C, but no further increase in the higher growth range, suggesting, that from 50 degrees C upward a shift to the exclusive production of thermostable protein occurs. Furthermore, the stability of alanine dehydrogenase and pyruvate kinase was found to increase substantially in presence of their substrates. In contrast, substrate-mediated stabilization was very weak with glucose-6-phosphate dehydrogenase and totally absent with acetate kinase, isocitrate dehydrogenase and myokinase. A comparison with previous observations with the same enzymes from Bacillus flavothermus showed, that enzymes from different organisms can have different thermal properties. Determination of the fatty acid composition of Streptomyces sp. cells, grown at different temperatures, showed relatively small alterations, with the main changes occurring between 37 degrees C and 40 degrees C.