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Research Paper |
Microbial Biochemistry and Genetics Unit, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892-4350, USA1
Department of Infectious Diseases, Childrens National Medical Center, Washington DC 20010-2970, USA2
Institut für Organische Chemie, Technische Universität Darmstadt,D-64287 Darmstadt, Germany3
Author for correspondence: John Thompson. Tel: +1 301 496 4083. Fax: +1 301 402 0396. e-mail: jthompson{at}dir.nidcr.nih.gov
Fusobacterium mortiferum utilizes sucrose [glucose-fructose in
(1
2) linkage] and its five isomeric
-D-glucosyl-D-fructoses as energy sources for growth. Sucrose-grown cells are induced for both sucrose-6-phosphate hydrolase (S6PH) and fructokinase (FK), but the two enzymes are not expressed above constitutive levels during growth on the isomeric compounds. Extracts of cells grown previously on the sucrose isomers trehalulose
(1
1), turanose
(1
3), maltulose
(1
4), leucrose
(1
5) and palatinose
(1
6) contained high levels of an NAD+ plus metal-dependent phospho-
-glucosidase (MalH). The latter enzyme was not induced during growth on sucrose. MalH catalysed the hydrolysis of the 6'-phosphorylated derivatives of the five isomers to yield glucose 6-phosphate and fructose, but sucrose 6-phosphate itself was not a substrate. Unexpectedly, MalH hydrolysed both
- and ß-linked stereomers of the chromogenic analogue p-nitrophenyl glucoside 6-phosphate. The gene malH is adjacent to malB and malR, which encode an EII(CB) component of the phosphoenolpyruvate-dependent sugar:phosphotransferase system and a putative regulatory protein, respectively. The authors suggest that for F. mortiferum, the products of malB and malH catalyse the phosphorylative translocation and intracellular hydrolysis of the five isomers of sucrose and of related
-linked glucosides. Genes homologous to malB and malH are present in both Klebsiella pneumoniae and the enterohaemorrhagic strain Escherichia coli O157:H7. Both these organisms grew well on sucrose, but only K. pneumoniae exhibited growth on the isomeric compounds.
Keywords: phospho-
-glucosidase, sucrose isomers, sucrose-6-phosphate hydrolase, Klebsiella pneumoniae, Escherichia coli O157:H7
Abbreviations: FK, fructokinase; G6P, glucose 6-phosphate; G6PDH, glucose-6-phosphate dehydrogenase; HK, hexokinase; 4-MU-
-G6P, 4-methylumbelliferyl
-D-glucopyranoside-6-phosphate; PEP:PTS, phosphoenolpyruvate-dependent sucrose:phosphotransferase system; pNP-
-G6P, p-nitrophenyl
-D-glucopyranoside 6-phosphate; pNP-ß-G6P, p-nitrophenyl ß-D-glucopyranoside 6-phosphate; S6PH, sucrose-6-phosphate hydrolase
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