Investigation of Thermolabile Variants of the Methanol and Methylamine Dehydrogenases of Methylophilus Methylotrophus and the Effect of an 11{middle dot}5 kbp Region of the Chromosome on the Stability of these Enzymes

Abstract

Summary: The thermal stabilities in vitro of the methylamine and methanol dehydrogenases of Methylophilus methylotrophus varied, depending on the conditions in which the organism was grown. Methylamine dehydrogenase activity was more stable in extracts of cells grown on methylamine plus NH+ 4 or on methanol plus methylamine than when methylamine provided the sole carbon and nitrogen source. In contrast, the methanol dehydrogenase activity in extracts of methylamine-grown cells was more stable than that from cells grown on medium containing methanol with either NH+ 4 or methylamine as the nitrogen source. The stability of thermolabile forms of the dehydrogenases present in extracts of mutants which have temperature-sensitive defects in the oxidation of C1 compounds also varied with the growth conditions. When cosmid pAD833, which complemented these temperature-sensitive mutants, was present during growth of the wild-type strain on methylamine, the thermal stabilities of both methylamine and methanol dehydrogenases increased. However, the effects of subclones of pAD833 were complex and our results indicate that the DNA region carried on this cosmid encodes gene products which can both increase and decrease the in vitro thermal stability of enzymes involved in C1 metabolism.