Ethanolamine Deaminase, a Cobamide Coenzyme-dependent Enzyme

Abstract

Abstract Ethanolamine deaminase, a clostridial enzyme that catalyzes the cobamide coenzyme-dependent conversion of ethanolamine to ammonia and acetaldehyde, has been obtained as a homogeneous protein. Isolation of the relatively stable enzyme was facilitated by its unique lack of solubility in solutions with an ionic strength greater than 0.11. The specific activities of apparently homogeneous preparations isolated from different batches of cells are slightly different. A spectrophotometric assay for the detection of less than 1 µg of purified enzyme was developed by coupling the formation of acetaldehyde in the deaminase reaction with DPNH oxidation in the presence of added alcohol dehydrogenase. The deaminase reaction has an absolute requirement for cobamide coenzyme. The apparent Km values for α-(5,6-dimethylbenzimidazolyl)cobamide coenzyme, α-benzimidazolyl)cobamide coenzyme, and α-(adenylyl)cobamide coenzyme are 1.5 x 10-6, 1.9 x 10-7, and 7.7 x 10-6 m, respectively. Of several compounds tested, only ethanolamine is a substrate for the enzyme. Potassium ion is required for catalytic activity, whereas Li+ and Na+ are competitive inhibitors. The pH optimum for the reaction is 6.8 to 8.2. p-Chloromercuriphenylsulfonate inhibited the deaminase 46% at 3 x 10-4 m. Like the dioldehydrase described by Lee and Abeles (15), ethanolamine deaminase is inactivated by incubation with cobamide coenzyme in the absence of substrate, and both the deaminase and dioldehydrase reactions have a detectable lag period at low levels of cobamide coenzyme.