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J Bacteriol, May 1998, p. 2337-2344, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Substrate Specificities of Hybrid Naphthalene and 2,4-Dinitrotoluene Dioxygenase Enzyme Systems

Rebecca E. Parales,* Matthew D. Emig, Nancy A. Lynch,dagger and David T. Gibson

Department of Microbiology and Center for Biocatalysis and Bioprocessing, University of Iowa, Iowa City, Iowa 52242

Received 19 December 1997/Accepted 26 February 1998

Bacterial three-component dioxygenase systems consist of reductase and ferredoxin components which transfer electrons from NAD(P)H to a terminal oxygenase. In most cases, the oxygenase consists of two different subunits (alpha  and beta ). To assess the contributions of the alpha  and beta  subunits of the oxygenase to substrate specificity, hybrid dioxygenase enzymes were formed by coexpressing genes from two compatible plasmids in Escherichia coli. The activities of hybrid naphthalene and 2,4-dinitrotoluene dioxygenases containing four different beta  subunits were tested with four substrates (indole, naphthalene, 2,4-dinitrotoluene, and 2-nitrotoluene). In the active hybrids, replacement of small subunits affected the rate of product formation but had no effect on the substrate range, regiospecificity, or enantiomeric purity of oxidation products with the substrates tested. These studies indicate that the small subunit of the oxygenase is essential for activity but does not play a major role in determining the specificity of these enzymes.

* Corresponding author. Mailing address: Department of Microbiology, 3-730 BSB, University of Iowa, Iowa City, IA 52242. Phone: (319) 335-7982. Fax: (319) 335-9999. E-mail: rebecca-parales{at}uiowa.edu.

dagger Present address: Department of Pathology, University of Iowa, Iowa City, IA 52242.

J Bacteriol, May 1998, p. 2337-2344, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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