Ethanolamine deaminase

Among the first enzymes studied by EPR were ethanolamine deaminase and AdoCbl-dependent ribonucleotide reductase (Babior et al., 1974 Orme-Johnson et ah, 1974). The EPR spectrum of ethanolamine deaminase was extensively characterized in the presence of 2-aminopropanol, which is a slow substrate for the enzyme. It exhibits a broad feature at g = 2.34 attributed to Cbl(II), and a sharp doublet at g = 2.01 attributed to an organic radical. Using isotopically-labeled substrates, the organic radical was identified as the C-1 radical of 2-aminopropanol (Babior et al., 1974). The doublet splitting was attributed to dipolar coupling of the Co(II) spin with the substrate radical and the distance between cobalt and the substrate radical was calculated to be about 6. Thus, these experiments yielded the first structural information on the active site of a Bn enzyme. 

B12-dependent ribonucleotide reductase was the first enzyme for which the rate of AdoCbl homolysis was examined. Pioneering studies by Blakely and co-workers established that a homolytic mechanism was indeed operating, as opposed to heterolytic cleavage to give Co(I), and that the rate of homolysis (k= 38s" ) was kinetically competent (Tamao and Blakely, 1973). Subsequently, the kinetic competency of CooC cleavage in ethanolamine deaminase was established (Hollaway et al., 1978), and, as discussed below, homolysis has been found to be far more rapid than turnover for all the enzymes so far examined. 

Harkins and Grissom have made the interesting observation that catalysis by ethanolamine deaminase is affected by external magnetic fields (Harkins and Grissom, 1994). It is expected that reactions involving free radicals may be sensitive to magnetic fields, and there are prior examples in the chemical literature (for a review see Steiner and Ulrich, 1989), but... 

S.-C. (1999) Identification of a rearranged-substrate, product radical intermediate and the contribution of a product radical trap in vitamin B12 coenzyme-dependent ethanolamine deaminase catalysis, J. Am. Chem. Soc. 121, 10522-10528. 

Cobalamin analogs inhibit ethanolamine deaminase. (Ethanolamine is an industrial solvent that selectively absorbs the acid gases COj and H2S.)... 

Growth of several species of bacteria induces the production of EAL, also known as ethanolamine deaminase, which catalyzes the adenosylcobalamin-dependent deamination of ethanolamine to acetaldehyde and ammonium ion according to Equation (10). 

Table IV shows how Arigoni interpreted his results 4). The diol is converted to the gem-diol through a series of rearrangements, in which it was postulated that the B12 coenzyme was involved as an intermediate hydrogen acceptor. The gem-diol is then stereospecifically dehydrated. If the enzyme has first seen the S isomer, it removes one of the —OH groups if it has first seen the R-isomer, it removes the other —OH group. If we accept this intermediate, we have a similarity between all of the reactions—Le., a rearrangement. With the ethanolamine deaminase, there is some evidence which is in further agreement with this type of an intermediate.

Another B12 coenzyme-dependent dehydrase converts glycerol to 3-hydroxypropionaldehyde. A B12-dependent ethanolamine deaminase catalyzes the irreversible conversion of ethanolamine to acetaldehyde and ammonia. A corrinoid protein participates in methyl transfer reactions and methane formation by bacteria producing methane. Corrinoid proteins are also involved in acetate synthesis from carbon dioxide. 

Deaminase. The adenosyl-cobamide-dependent enzyme ethanolamine ammonia lyase (from Clostridia) transforms the vicinal amino alcohol ethanolamine to acetaldehyde (with liberation of ammonia) (see Table 2, entry 3). Isotopic labeling has shown that the reaction is initiated by abstraction of a hydrogen atom from the hydroxymethylene group the reactive radical is provided from homolysis of the (Co-C)-bond of protein-bound coenzyme 2 (76). Magnetic field effects have provided independent evidence for the existence of caged radicals (85). 

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