Abstract
We have paid much attention to screen and characterize enzymes from hyperthermophiles for analysis of their metabolic pathways of amino acids and utilization of the enzymes as the functional element for biosensor. In this review, we introduce two kinds of enzymes, FAD-dependent L-proline dehydrogenase complex and PLP-dependent amino acid racemase, from hyperthermophilic archaea. Two different FAD-dependent L-proline dehydrogenase activities were detected in the screening process of stable dye-linked dehydrogenase as specific element for electrochemical biosensor. The first enzyme found in Thermococcus profundus formed α β γ δ structure with not only proline dehydrogenase activity but also NADH dehydrogenase activity. We have succeeded in the construction of DNA sensing system using this enzyme. The second one from Pyrococcus horikoshii formed α4β4 structure and had FAD, FMN, ATP and Fe as cofactors. On the other hand, PLP-dependent amino acid racemase with broad substrate specificity was found in the process of investigation into D-amino acid utilization in the growth of P. horikoshii. Furthermore, we found another amino acid racemase specific for Ala and Ser by functional analysis of the homologs of the amino acid racemase. Because the genes of both dehydrogenases and racemases are widely conserved in the genomes of Pyrococcus and Thermococcus species, these enzymes may play important roles in the amino acid metabolisms.
