The chitin catabolic cascade in the marine bacterium Vibrio furnissii. Characterization of an N,N'-diacetyl-chitobiose transport system.
The disaccharide N,N'-diacetyl-chitobiose, (GlcNAc)2, is critical in chitin dissimilation by Vibrio furnissii and, as reported here, is taken up by a specific permease. Since (GlcNAc)2 is rapidly catabolized by V. furnissii, a non-hydrolyzable thioglycoside analogue was used: methyl beta-N,N'-[3H]diacetyl-thiochitobioside (Me-[3H]TCB). Me-TCB and TCB substitute for (GlcNAc)2 as chemoattractants and inducers of beta-N-acetylglucosaminidase activity. The [3H]Me-TCB uptake system was induced only by (GlcNAc)2 and by (GlcNAc)n that can be converted to (GlcNAc)2. The Km for [3H]Me-TCB uptake was </=1 microM and was not affected by Na+ or K+. Uptake appeared to be unidirectional, and in 0.4 M sucrose (+/- K+) the cells accumulated [3H]Me-TCB until it was depleted from the medium, giving an internal concentration of 0.1 M and an internal/external ratio > 1,000. The only effective inhibitors of uptake were: (GlcNAc)n, n = 2-4 > cellobiose > (GlcNAc)5. In 50% artificial sea water (or sucrose/Na+), [3H]Me-TCB accumulation attained a constant steady state level because of efflux, a Na+-dependent process. The physiological implications of these results are considered.
Keyhani
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Department of Biology and the McCollum-Pratt Institute, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
Wang
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LX
Lee
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YC
Roseman
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S
D001693:Biological Transport, Active; D002686:Chitin / Q000378:metabolism*; D004187:Disaccharides / Q000378:metabolism*; D007700:Kinetics; D008956:Models, Chemical; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D014733:Vibrio / Q000378:metabolism*; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
D004187:Disaccharides; C103151:methyl beta-N,N'-diacetylthiochitobiose; D002686:Chitin; C010913:N,N-diacetylchitobiose; D012964:Sodium; D001619:beta-N-Acetylhexosaminidases; D011188:Potassium