CRYSTALLIZATION OF THE ALANINE DEHYDROGENASE FROM PHORMIDIUM-LAPIDEUM

Amino-acid dehydrogenases catalyse the interconversion of their respec tive amino acids to the corresponding keto acid, with concomitant redu ction of NAD or NADP. The enzymes phenylalanine, glutamate, leucine an d valine dehydrogenase all share a similar three-dimensional subunit s tructure and a high degree of sequence similarity, indicating that the y belong to an enzyme superfamily related by divergent evolution. In c ontrast, alanine dehydrogenase shows no sequence similarity with any o f these enzymes despite catalysing a reaction with the same chemistry and thus it is predicted that it possesses a different three-dimension al structure. The alanine dehydrogenase from Phormidium lapideum has b een crystallized in space group R32, cell dimensions a = b = 123.1 and c = 184.8 Angstrom, with a monomer in the asymmetric unit. The struct ure determination of this enzyme will shed light on how nature has evo lved two different systems to carry out the same reaction.