BIOCHEMICAL-CHARACTERIZATION OF A HALOALCOHOL DEHALOGENASE FROM ARTHROBACTER-ERITHII H10A

Arthrobacter erithii H10a possesses two enzymes capable of catalyzing the dehalogenation of vicinal halohydrins which have been designated a s dehalogenases DehA and DehC. The DehA dehalogenase demonstrated grea ter activity toward 1,3-dichloro-2-propanol (1,3-DCP) while the DehC d ehalogenase showed higher activity toward 3-chloro-1,2-propanediol (3- CPD) and brominated alcohols. The DehA dehalogenase was composed of tw o non-identical subunits (relative molecular mass of 31.5 and 34 kDa) which probably associate with other proteins to form a large catalytic ally active protein of 200 kDa. The two subLmits were purified and the amino acid sequence of their tryptic digests determined The DehA enzy me 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 degrees C and a broad pH optimum over the range 8.5-10.5. The apparent K-m and V-max values for dehalogenation o f 1,3-DCP and 3-CPD were 0.105 mM and 223 mu mol min(-1) mg(-1); and 2 .366 mM and 1.742 mu mol min(-1) mg(-1) respectively. The enzyme was i nhibited 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 demon strated 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 co mpared to those of previously reported haloalcohol dehalogenases and d iscussed in terms of diversity of this type of dehalogenase. (C) 1998 Elsevier Science Inc.