Crystallization of the alanine dehydrogenase from Phormidium lapideum.

Amino-acid dehydrogenases catalyse the interconversion of their respective amino acids to the corresponding keto acid, with concomitant reduction of NAD or NADP. The enzymes phenylalanine, glutamate, leucine and valine dehydrogenase all share a similar three-dimensional subunit structure and a high degree of sequence similarity, indicating that they belong to an enzyme superfamily related by divergent evolution. In contrast, alanine dehydrogenase shows no sequence similarity with any of these enzymes despite catalysing a reaction with the same chemistry and thus it is predicted that it possesses a different three-dimensional structure. The alanine dehydrogenase from Phormidium lapideum has been crystallized in space group R32, cell dimensions a = b = 123.1 and c = 184.8 A, with a monomer in the asymmetric unit. The structure determination of this enzyme will shed light on how nature has evolved two different systems to carry out the same reaction.