Overproduction of thermostable leucine dehydrogenase of Bacillus stearothermophilus and its one‐step purification from recombinant cells of Escherichia coli

We have cloned the leucine dehydrogenase (EC 1.4.1.9) gene from a thermophile, Bacillus stearothermophilus, into Escherichia coli MV1184 with a vector plasmid, pUC119. The cloned cells produced a large amount of the thermostable enzyme, which corresponds to about 60% of the total soluble protein. The enzyme was purified to more than 95% homogeneity by only one step, heat treatment of the cell‐extracts, with an average yield of 75 mg/g of wet cells (obtained from 100 ml of the culture).