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First published online February 4, 2005
Journal of Experimental Biology 208, 637-646 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01428
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Arginine kinase in the demosponge Suberites domuncula: regulation of its expression and catalytic activity by silicic acid

Sanja Perovic-Ottstadt1, Matthias Wiens1, Heinz-C. Schröder1, Renato Batel2, Marco Giovine3, Anatoli Krasko1, Isabel M. Müller1 and Werner E. G. Müller1,*

1 Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, D-55099 Mainz, Germany,
2 Center for Marine Research, `Ruder Boskovic' Institute, HR-52210 Rovinj, Croatia
3 CNR-Direzione Progetto Finalizzato Biotecnologie, Via Leon Battista Alberti 4, I-16132 Genova, Italy

* Author for correspondence (e-mail: wmueller{at}uni-mainz.de)

Accepted 1 December 2004

In Demospongiae (phylum Porifera) the formation of the siliceous skeleton, composed of spicules, is an energetically expensive reaction. The present study demonstrates that primmorphs from the demosponge Suberites domuncula express the gene for arginine kinase after exposure to exogenous silicic acid. The deduced sponge arginine kinase sequence displays the two characteristic domains of the ATP:guanido phosphotransferases; it can be grouped to the `usual' mono-domain 40 kDa guanidino kinases (arginine kinases). Phylogenetic studies indicate that the metazoan guanidino kinases evolved from this ancestral sponge enzyme; among them are also the `unusual' two-domain 80 kDa guanidino kinases. The high expression level of the arginine kinase gene was already measurable 1 day after addition of silicic acid by northern blot, as well as by in situ hybridization analysis. Parallel determinations of enzyme activity confirmed that high levels of arginine kinase are present in primmorphs that had been exposed for 1-5 days to silicic acid. Finally, transmission electron-microscopical studies showed that primmorphs containing high levels of arginine kinase also produce siliceous spicules. These data highlight that silicic acid is an inorganic morphogenetic factor that induces the expression of the arginine kinase, which in turn probably catalyzes the reversible transfer of high-energy phosphoryl groups.

Key words: sponge, arginine kinase, siliceous spicule, Suberites domuncula, primmorph, energy metabolism


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