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Biochemical Characterization of a Haloalcohol Dehalogenase from Arthrobacter erithii H10a

1998; Elsevier BV; Volume: 22; Issue: 7 Linguagem: Inglês

10.1016/s0141-0229(97)00254-8

1879-0909

H.M.S. Assis, Paul Sallis, Alan T. Bull, David J. Hardman,

Biofuel production and bioconversion

Arthrobacter erithii H10a possesses two enzymes capable of catalyzing the dehalogenation of vicinal halohydrins which have been designated as dehalogenases DehA and DehC. The DehA dehalogenase demonstrated greater activity toward 1,3-dichloro-2-propanol (1,3-DCP) while the DehC dehalogenase showed higher activity toward 3-chloro-1,2-propanediol (3-CPD) and brominated alcohols. The DehA dehalogenase was composed of two non-identical subunits (relative molecular mass of 31.5 and 34 kDa) which probably associate with other proteins to form a large catalytically active protein of 200 kDa. The two subunits were purified and the amino acid sequence of their tryptic digests determined. The DehA enzyme catalyzed the conversion of vicinal halohydrins to epoxides and the reverse reaction in the presence of an excess of halogen. This enzyme had maximum activity at 50°C and a broad pH optimum over the range 8.5–10.5. The apparent Km and Vmax values for dehalogenation of 1,3-DCP and 3-CPD were 0.105 mm and 223 μmol min−1 mg−1; and 2.366 mm and 1.742 μmol min−1 mg−1, respectively. The enzyme was inhibited by 2-chloroacetic acid (MCA) and 2,2-dichloroacetic acid (DCA). The inhibition pattern suggested a mixed type inhibition which was predominantly uncompetitive. Amino acid modification experiments demonstrated that one or more cysteine and arginine residues are likely to be involved in catalysis or play an important role in the maintenance of the enzyme structure. The characteristics of the DehA enzyme are compared to those of previously reported haloalcohol dehalogenases and discussed in terms of diversity of this type of dehalogenase.