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FEBS Lett. 2003 Apr 10;540(1-3):96-100.

Protein transport via the cpTat pathway displays cooperativity and is stimulated by transport-incompetent substrate.

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Division of Biological Sciences, Section of Plant Biology, University of California, One Shields Avenue, Davis, CA 95616, USA.


Kinetic analyses of cpTat-mediated protein transport across the thylakoid membrane were conducted, revealing three important characteristics of this translocation pathway. First, transport via the cpTAT system displays a non-Michaelis-Menten, sigmoidal rate-substrate relationship with an apparent Hill coefficient of 1.80, indicative of positive homotropic cooperativity. Second, the presence of transport-incompetent substrates was found not to competitively inhibit the translocation of transport-competent substrates. However, the presence of low concentrations of transport-incompetent protein enhances the transport of wild type substrate. Together, these findings suggest that interaction between Tat machinery components and both transport-competent and transport-incompetent protein may elicit a cooperative effect on the translocation rate.

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