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Appl. Environ. Microbiol. doi:10.1128/AEM.02703-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

NADP(H) phosphatase activities in archaeal inositol monophosphatase and eubacterial 3'-phosphoadenosine 5'-phosphate phosphatase

Department of Basic and Applied Molecular Biotechnology, Division of Food and Biological Science, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan

^* To whom correspondence should be addressed. Email: kmurata{at}kais.kyoto-u.ac.jp.

	Abstract

NADP(H) phosphatase has not been identified in eubacteria and eukaryotes. In archaea, MJ0917 of hyperthermophilic Methanococcus jannaschii is a fusion protein comprising NAD kinase and an inositol monophosphatase homologue that exhibits high NADP(H) phosphatase activity (Kawai, S., C. Fukuda, T. Mukai, and K. Murata. 2005. J. Biol. Chem. 280:39200-39207). In this study, we showed that the other archaeal inositol monophosphatases--MJ0109 of M. jannaschii and AF2372 of hyperthermophilic Archaeoglobus fulgidus--exhibit NADP(H) phosphatase activity in addition to the already-known inositol monophosphatase and fructose-1,6-bisphosphatase activities. Kinetic values for NADP⁺ and NADPH of MJ0109 and AF2372 were comparable to those for inositol monophosphate and fructose-1,6-bisphosphate. This implies that the physiological role of the 2 enzymes is that of NADP(H) phosphatase. Further, the 2 enzymes showed inositol polyphosphate 1-phosphatase activity but not 3'-phosphoadenosine 5'-phosphate phosphatase activity. The inositol polyphosphate 1-phosphatase activity of archaeal inositol monophosphatase was considered to be compatible with the similar tertiary structures of inositol monophosphatase, fructose-1,6-bisphosphatase, inositol polyphosphate 1-phosphatase, and 3'-phosphoadenosine 5'-phosphate phosphatase. Based on this fact, we found that 3'-phosphoadenosine 5'-phosphate phosphatase (CysQ) of Escherichia coli exhibited NADP(H) phosphatase and fructose-1,6-bisphosphatase activities, although inositol monophosphatase (SuhB) and fructose-1,6-bisphosphatase (Fbp) of E. coli did not exhibit any NADP(H) phosphatase activity. However, the kinetic values of CysQ and the known phenotype of the cysQ mutant indicated that CysQ functions physiologically as 3'-phosphoadenosine 5'-phosphate phosphatase rather than as NADP(H) phosphatase.