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J. Biol. Chem., Vol. 279, Issue 49, 51193-51202, December 3, 2004

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The H⁺-pyrophosphatase of Rhodospirillum rubrum Is Predominantly Located in Polyphosphate-rich Acidocalcisomes^*

Manfredo Seufferheld, Christopher R. Lea, Mauricio Vieira, Eric Oldfield, and Roberto Docampo¶

From the Laboratory of Molecular Parasitology, Department of Pathobiology and Center for Zoonoses Research, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802 and the Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Acidocalcisomes are acidic, calcium storage compartments with a H⁺ pump located in their membrane that have been described in several unicellular eukaryotes, including trypanosomatid and apicomplexan parasites, algae, and slime molds, and have also been found in the bacterium Agrobacterium tumefaciens. In this work, we report that the H⁺-pyrophosphatase (H⁺-PPase) of Rhodospirillum rubrum, the first enzyme of this type that was identified and thought to be localized only to chromatophore membranes, is predominantly located in acidocalcisomes. The identification of the acidocalcisomes of R. rubrum was carried out by using transmission electron microscopy, x-ray microanalysis, and immunofluorescence microscopy. Purification of acidocalcisomes using iodixanol gradients indicated co-localization of the H⁺-PPase with pyrophosphate (PP_i) and short and long chain polyphosphates (polyPs) but a lack of markers of the plasma membrane. polyP was also localized to the acidocalcisomes by using 4',6'-diamino-2-phenylindole staining and identified by using ³¹P NMR and biochemical methods. Calcium in the acidocalcisomes increased when the bacteria were incubated at high extracellular calcium concentrations. The number of acidocalcisomes and chromatophore membranes as well as the amounts of PP_i and polyP increased when bacteria were grown in the light. Taken together, these results suggest that the H⁺-PPase of R. rubrum has two distinct roles depending on its location acting as an intracellular proton pump in acidocalcisomes but in PP_i synthesis in the chromatophore membranes.

Received for publication, June 2, 2004 , and in revised form, September 9, 2004.

^* This work was supported in part by National Institutes of Health Grants AI23259 (to R. D.) and GM50694 (to E. O.) and by funds from the Illinois Governor Venture Technology Fund (to R. D.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains a supplemental movie.

^¶ To whom correspondence should be addressed: Laboratory of Molecular Parasitology, Dept. of Pathobiology and Center for Zoonoses Research, University of Illinois at Urbana-Champaign, 2001 South Lincoln Ave., Urbana, IL 61802. Tel.: 217-333-3845; Fax: 217-244-7421; E-mail: rodoc{at}uiuc.edu.

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