S-adenosyl-L-homocysteine hydrolase from Xenopus laevis--identification, developmental expression and evolution

S-Adenosyl-L-homocysteine hydrolase (EC 3.3.1.1) is an important enzyme in the trans-sulphuration pathway, mediating the conversion of S-adenosyl-L-homocysteine to adenosine and L-homocysteine. We have identified a cDNA clone from Xenopus laevis, encoding a protein of 433 aa, which is highly conserved with S-Adenosyl-L-homocysteine hydrolases (Adohcyases) from other species. Expression of Adohcyase mRNA in X.laevis tadpoles is detectable from developmental Stage 27 onwards. Phylogenetic analysis of available Adohcyase sequences indicates that species cluster essentially as predicted from morphological data. Furthermore, we estimate that S-adenosyl-L-homocysteine hydrolase is evolving very slowly, almost 10 times slower than the average rate.