The Mechanism of Action of Ethanolamine Deaminase: I. STUDIES WITH ISOTOPIC HYDROGEN AND OXYGEN

Abstract

Deuterated and tritiated ethanolamine and H218O were used to study the mechanism of the conversion of ethanolamine to acetaldehyde and ammonia catalyzed by ethanolamine deaminase, a coenzyme-B12-dependent enzyme. An isotope effect of 6.8 was shown in the deamination of deuterated ethanolamine, indicating that the rate-limiting step involves the transfer of hydrogen. However, the fact that the tritium isotope effect was only 5.8 in the face of the deuterium isotope effect of 6.8 suggested the possibility of a large secondary isotope effect in the reactions conducted with deuterated substrate. The conversion of ethanolamine to acetaldehyde was shown to take place with the transfer of hydrogen from the carbinol carbon to the amino carbon without exchange with water. Both intra- and intermolecular hydrogen transfer appear to take place. Moreover, it was shown that, in carrying out this transfer, the enzyme was capable of distinguishing between the 2 hydrogen atoms on the carbinol carbon. Experiments with deuterated ethanolamine confirmed the previous observation that the carbinol carbon of the substrate becomes the carbonyl carbon of acetaldehyde. Experiments conducted in H218O showed that the oxygen atom of the substrate is retained in the product.