Methanol dehydrogenase (MDH) is a water soluble quinoprotein that catalyzes the oxidation of methanol as an important carbon source in methylotrophic bacteria. A rapid method for the purification of MDH from McthYlobacierhon extol-quells AMI was developed using a single cation exchange chromatographic step, followed by ultratiltration for final purification, enzyme concentration, and buffer exchange. MDH was obtained in an excellent overall yield with a final enzyme purity of greater than 97%. Storage at -80 degrees C in 20 mM phosphate buffer, pH 7.0, showed only a negligible loss of enzyme activity after six months. (c) 2005 Elsevier Inc. All rights reserved.