[Mutations in the alpha-amylase gene of Bacillus amyloliquefaciens, leading to a decrease in the temperature of protein inactivation].

Alpha-amylase genes of Bacillus amyloliquefaciens, coding proteins with reduced thermostability, had been obtained as a result of hydroxylamine mutagenesis. Temperature, pH and starch concentration dependences of two mutant alpha-amylases were investigated. The synthesis of the alpha-amylases by several B. subtilis strains with different levels of extracellular proteases was also studied. The mutation containing fragments were localized and the structures of the mutations were determined. It was found that the decrease of thermostability of mutant No 141 was due to Asp to Asn change at the position No 194 of the mature protein, and for mutant No 191--due to Glu to Lys change at the position No 185.