Purification and characterization of an activator protein for methanol dehydrogenase from themotolerant Bocillus spp

All thermotolerant methanol-utilizing Bacillus spp. investigated by us possess a NAD-dependent methanol dehydrogenase (MDH) activity which is stimulated by a protein present in the soluble fraction of Bacillus sp. C1 cells. This activator protein was purified to homo-geneity from B a ~ ~ l l ~ sp. C l cells grown at a low dilution rate in a methanol-limited chemostat culture. The native activator protein (M;. = 50,000) is a dimer of M, = 27,000 subunits. The N-terminal amino acid sequence revealed no significant similarity with any published sequences. Stimulation of MDH activity by the activator protein required the presence of Mg2+ ions. Plots of specific MDH activity versus activator protein concentration revealed Michaelis-Menten type kinetics. In the presence of activator protein, MD