Open channel-like behavior of reduced carrier models.
Previous theoretical analyses have demonstrated that some extended channel models can exhibit carrier kinetics, even for the case of models where the transporter does not experience any conformational change. The purpose of this work is to explore the inverse situation, that is, the finding of channel-like transport properties in well-defined carrier models. This approximate behavior has been previously encountered for the case that rapid equilibrium is established between the empty carrier states. This study explores another situation in which a typical carrier can exhibit open channel-like kinetic properties, namely, the reduction of a classical four-state simple carrier model for the case that one of the empty states is a transient intermediate. For this case I analyze here if, for some conditions, the kinetics of the three-state reduced model can be satisfactorily approximated by a channel description. The analysis performed here derives conditions under which this reduced model exhibits channel-like transport kinetics. The work is illustrated by the numerical studies of two comparative examples: one corresponding to a carrier satisfying the necessary conditions for the channel-like behavior, and another for a carrier not meeting those conditions. The finding that a well-defined carrier model may exhibit channel-like transport properties represents a further argument in favor of the concept that typical channels and carriers are particular cases of more general mechanisms of facilitative transport.
Hernández
J A
JA
Sección Biofísica, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay.
D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological
D002352:Carrier Proteins; D007473:Ion Channels