We recently had a new paper accepted by the JBC, describing a detailed
kinetic model and control analysis of the bacterial phosphotransferase
system in enteric bacteria. The paper can be viewed online (JCB papers in
press) for free at the following URL:
http://www.jbc.org/cgi/reprint/M002461200v1
Abstract:
The kinetic parameters in vitro of the components of the
phosphoenolpyruvate:glucose phosphotransferase system (PTS) in enteric
bacteria were collected. To address the issue whether the behavior in vivo
of the PTS can be understood in terms of these enzyme kinetics, a detailed
kinetic model was constructed. Each overall phosphotransfer reaction was
separated into two elementary reactions, the first entailing association of the
phosphoryl donor and acceptor into a complex, and the second entailing
dissociation of the complex into dephosphorylated donor and
phosphorylated acceptor. Literature data on the Km values and association
constants of PTS proteins for their substrates, as well as equilibrium and
rate constants for the overall phosphotransfer reactions, were related to the
rate constants of the elementary steps in a set of equations; the rate constants
could be calculated by solving these equations simultaneously. No kinetic
parameters were fitted. As calculated by the model, the kinetic parameter
values in vitro could describe experimental results in vivo when varying
each of the PTS protein concentrations individually whilst keeping the other
protein concentrations constant. Using the same kinetic constants, but
adjusting the protein concentrations in the model to those present in cell-free
extracts, the model could reproduce experiments in vitro analysing the
dependence of the flux on the total PTS protein concentration. For modeling
conditions in vivo it was crucial that the PTS protein concentrations be
implemented at their high in vivo values. The model suggests a new
interpretation of results hitherto not understood: in vivo, the major fraction
of the PTS proteins may exist as complexes with other PTS proteins or
boundary metabolites, whereas in vitro, the fraction of complexed proteins
is much smaller.
----------
Regards,
Johann
--
Johann M. Rohwer
Dept. of Biochemistry, Univ. of Stellenbosch
Private Bag X1, 7602 Matieland
SOUTH AFRICA
Tel.: +27-21-8085843
Fax: +27-21-8085863
E-mail: jr at maties.sun.ac.za
WWW: http://www.sun.ac.za/biochem/
--
---
