Mathematical Treatment of Transport Data of Bacterial Transport Systems to Estimate Limitation in Diffusion through the Outer Membrane
✍ Scribed by CAROLA TRALAU; GERHARD GRELLER; MARKUS PAJATSCH; WINFRIED BOOS; ERICH BOHL
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 262 KB
- Volume
- 207
- Category
- Article
- ISSN
- 0022-5193
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✦ Synopsis
Bacterial transport systems are traditionally treated as enzymes exhibiting a saturable binding site giving rise to an apparent K K of transport, whereas the maximal rate of transport is regarded equivalent to the < K?V of enzymatic reactions. Thus, the Michaelis}Menten theory is usually applied in the analysis of transport data and K K and < K?V are derived from the treatment of data obtained from the rate of transport at varying substrate concentrations. Such an analysis tacitly assumes that the substrate recognition site of the transport system is freely accessible to substrate. However, this is not always the case. In systems endowed with high a$nity in the M range or those recognizing large substrates or those exhibiting high < K?V , the di!usion through the outer membrane may become rate determining, particularly at low external substrate concentrations. In such a situation the dependence of the overall rate of transport (from the medium into the cytoplasm) on the substrate concentration in the medium will no longer follow Michaelis}Menten kinetics. By analysing the deviation of transport data from the corresponding ideal Michaelis}Menten plot we developed a method that allows us to determine di!usion limitation through the outer membrane. The method allows us to "nd the correct K K of the transport system functioning at the inner membrane even under conditions of strong di!usion limitation through the outer membrane. The model was tested and validi"ed with the Escherichia coli binding protein-dependent ABC transporter for maltose. The corresponding systems for sn-glycerol-3-phospate of Escherichia coli and the -cyclodextrin transport of Klebsiella oxitoca were used as test systems.
2000 Academic Press C. TRALAU E¹ A¸.