Gene Expression and Characterization of a Third Type of Dye-Linked L-Proline Dehydrogenase from the Aerobic Hyperthermophilic Archaeon, Aeropyrum pernix

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A third novel type of dye-linked L-proline dehydrogenase (LPDH) has recently been found in the hyperthermophilic archaeon, Pyrobaculum calidifontis, by Satomura et al. The gene encoding the enzyme homologue was identified in the aerobic hyperthermophilic archaeon, Aeropyrum pernix. The gene was successfully expressed in Escherichia coli, and the product was purified to homogeneity and characterized. The expressed enzyme was highly thermostable LPDH having a molecular mass of about 88 kDa and a homodimeric structure. The preferred substrate for the enzyme was L-proline with 2,6-dichloroindophenol (DCIP) as the electron acceptor. However, the enzyme did not utilize ferricyanide as the electron acceptor, in contrast to all other known LPDHs. The electrochemical determination of L-proline at concentrations from 0 to 0.7 mM was achieved by using A. pernix LPDH. A phylogenetic analysis revealed A. pernix LPDH to be clustered with the third type of LPDHs, and to be clearly separated from the clusters of previously known heterooligomeric LPDHs.