Biology Reference
In-Depth Information
sugar
EIIA
EI
PEP
~P
EIIB
~P
HPr
EIIC
~P
pyruvate
EIIB
EI
HPr
~P
EIIA
sugar
~P
FIGURE 14.17
The bacterial PTS system for glucose transport
[27]
.
E. IONOPHORES
The term ionophore means 'ion bearer'. Ionophores are small, lipid-soluble molecules,
usually of microbial origin, whose function is to conduct ions across membranes
[28,29]
.
They are facilitated diffusion carriers that transport ions down their electrochemical gradient.
Ionophores can be divided into two basic classes: channel formers and mobile carriers
(
Figure 14.18
)
[30]
. Channel formers are long lasting, stationary structures that allow many
ions to rapidly flow across a membrane. Mobile carriers bind to an ion on one side of
a membrane, dissolve in the membrane bilayer, and release the ion on the other side. They
can only carry one ion at a time. Four representative ionophores will be discussed, the K
รพ
ionophore valinomycin, the proton ionophore 2,4-dinitrophenol, synthetic crown ethers,
and the channel forming ionophore nystatin (
Figure 14.19
).
transported ion
lipid
bilayer
channel
former
mobile ion
carrier
FIGURE 14.18
Two basic types of ionophores, channel formers (left) and mobile carriers (right)
[30]
.