Enzyme thermostability is a transformable property between Bacillus spp

WE are interested in the evolutionary adaptation of enzymes and their control systems in different environments. We have studied the thermostability of organisms and their enzymes with DNA-mediated transformation between Bacillus spp. using an essential biosynthetic enzyme as a well-defined biochemical marker. Purification and characterisation of the enzyme L -histidinol dehydrogenase (HDH), EC 1.1.1.23, from a range of temperature-adapted species 1,12 has shown that although they possess similar physical characteristics, Michaelis constants, molecular weights, subunit numbers and p H optima, they show vastly different temperature ranges of activity. Singleton and Amelunxen 2 conclude that present evidence is incompatible with any single theory of the mechanism of thermophily. There seems to be a general finding, however, that the amino acid sequence itself confers thermostability, either through disulphide bridge interaction, by an increased proportion of hydrophobic amino acids, or by an interaction with metallic ions giving an altered conformation.