Deamination of 2-aminopropanol by ethanolamine ammonia-lyase, an AdoCbl-requiring enzyme. Kinetics and isotope effects for the R and S enantiomers of the substrate.
Both (R)-2-aminopropanol and (S)-2-aminopropanol are substrates for ethanolamine ammonia-lyase, reacting to yield propionaldehyde and ammonia via a common enzyme-bound intermediate. (S)-Propanolamine shows a lower Km and a higher Vmax than the R enantiomer, indicating that the former is a substantially better substrate than the latter. From the isotope effects and other considerations, it appears that the rate-limiting step for (S)-propanolamine is the same as that for ethanolamine, namely, the transfer of hydrogen from the cofactor to the product. In contrast, isotope effects seen with (R)-propanolamine indicate that there are two rate-limiting steps, both located in the segment of the reaction mechanism which is unique to the R enantiomer. One of these is the transfer of hydrogen from the substrate to the cofactor. The other is a subsequent step whose rate is similar to that of the first hydrogen transfer step but which does not involve the rupture of a carbon-hydrogen bond. It is speculated that this second rate-limiting step may have to do with the migration of the amino group.
D000642:Ammonia-Lyases / Q000378:metabolism*; D003013:Clostridium / Q000201:enzymology*; D003038:Cobamides / Q000494:pharmacology*; D004981:Ethanolamine Ammonia-Lyase / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics; D008433:Mathematics; D011412:Propanolamines; D013379:Substrate Specificity
D003038:Cobamides; D011412:Propanolamines; D000642:Ammonia-Lyases; D004981:Ethanolamine Ammonia-Lyase; C000913:cobamamide