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Infect Immun, February 1998, p. 710-716, Vol. 66, No. 2
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Identification and Characterization of a Novel Extracellular Ferric Reductase from Mycobacterium paratuberculosis

Matthias Homuth,1 Peter Valentin-Weigand,1,* M. Rohde,2 and Gerald-F. Gerlach1

Institut für Mikrobiologie und Tierseuchen, Tierärztliche Hochschule Hannover, Hannover,1 and Division of Microbiology, GBF-National Research Centre for Biotechnology, Braunschweig,2 Germany

Received 22 July 1997/Returned for modification 8 October 1997/Accepted 20 November 1997

A novel extracellular mycobacterial enzyme was identified in the ruminant pathogen Mycobacterium paratuberculosis. The enzyme was capable of mobilizing iron from different sources such as ferric ammonium citrate, ferritin, and transferrin by reduction of the metal. The purified reductase had a calculated Mr of 17,000, was sensitive to proteinase K treatment, and had an isoelectric point of pH 9. Analysis of the amino acid composition revealed glycine, serine, asparagine (or aspartic acid), and glutamine (or glutamic acid) as the most frequently occurring residues. Enzymatic activity was highest at 37°C and between pH 5 and 10. The calculated Km and Vmax for ferric ammonium citrate were 0.213 mM and 0.345 mM min-1 mg-1, respectively. Using a specific antireductase antibody in immunoelectron microscopy, we were able to detect the enzyme associated with intracellular mycobacteria in naturally M. paratuberculosis-infected bovine tissue. We propose that the reductase of M. paratuberculosis represents an alternative strategy of mycobacteria to mobilize ferric iron and discuss its potential role in bacterial evasion of intracellular defense mechanisms.

* Corresponding author. Mailing address: Institut fuer Mikrobiologie und Tierseuchen, Tieraerztliche Hochschule Hannover, Bishofsholer Damm 15, D-30173 Hannover, Germany. Phone: 49 (511) 856 7362. Fax: 49 (511) 856 7697. E-mail: pvalenti{at}micro.tiho-hannover.de.




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