PURPOSE: To prepare a heat-resistant enzyme having high specific activity, in high efficiency, by completely sterilizing a transformed strain which can be obtained in large amount by cultivation, and reacting the product with a bacteriolytic enzyme.

CONSTITUTION: A transformed bacterial strain such as Thermus flavus AT62 strain is obtained by the insertion of a plasmid integrated with the gene of heat-resistant enzyme. Escherichia coli C600 strain is transformed to Escherichia coli F-74 strain (FERM-P No.6698) by plasmid PBR322 containing the gene of the heat-resistant L-alanine dehydrogenase of the above transformed bacterial strain. Thermus flavus AT62. The obtained F-74 strain is cultured, and the cultured cells are collected and suspended to obtain a cell suspension. The suspension or the above cultured liquid is heated to effect the complete sterilization of the bacterial cells, and the obtained killed cells are collected and suspended. A bacteriolytic enzyme or the enzyme and a surface active agent are added to the above suspension to dissolve the heat-resistant enzyme from the bacterial cell to the suspension.