Biomedical Engineering Reference
In-Depth Information
to lower level could in principle generate a force of up to 200 pN, one order of mag-
nitude higher than that developed by myosin and kinesin (
2003
; Schliwa and
Woehlke
2003
) .
It should be noted that the acid base-controlled mechanical motion in
14
9+
can
lead to interesting functions, such as the opening and closing of a large cavity and
the control of the positions and properties of the bipyridinium legs. Since this behav-
ior can be used to control the uptake and release of a guest molecule from the nano-
elevator, it is of interest for the development of drug delivery systems.
4
Hybrid Systems
Recent scientifi c advances in molecular biology, supramolecular chemistry, and
nanofabrication techniques have opened up the possibility of building functional
hybrid devices based on natural motors. One long-term objective of this research is
to utilize the fi nest attributes associated with the worlds of both biological and syn-
thetic materials for the creation of nanomechanical systems that are powered by
biological motors (Xi et al.
2005
) .
Hybrid molecular shuttle systems based on kinesin and microtubules (Sect.
2.3
)
were constructed (Hess et al.
2004
) by using two different approaches: either the
microtubules are fi xed to a surface and kinesin is moving similar to cars moving on
a highway and transporting kinesin-coated objects (Limberis and Stewart
2000
) or
the kinesin is bound to the surface and the microtubules are propelled by the kinesin
analogous to a linear motor (Hess et al.
2001
). An interesting application of the
second technique is a statistical approach to surface imaging using fl uorescent
microtubules moving as probe robots across a surface coated with kinesin (Hess
et al.
2002
) .
4.1
Light-Driven Production of ATP Within an Artifi cial
Photosynthetic Membrane
A multicomponent molecular system (tetrad) specifi cally designed to achieve pho-
toinduced charge separation was vectorially incorporated in the bilayer membrane
of a liposome. It was demonstrated (Steinberg-Yfrach et al.
1997
) that, by visible
light irradiation of this system under proper experimental conditions, protons were
pumped into the liposome from the outside water solution. In principle, such a pro-
ton-motive force generated by photons can be utilized to perform mechanical work.
This result was beautifully achieved (Steinberg-Yfrach et al.
1998
; Gust et al.
2001
)
by incorporating F
0
F
1
-ATP synthase, with the ATP-synthesizing portion extending
out into the external aqueous solution in liposomes containing the components of
the proton-pumping photocycle. Irradiation of the membrane with visible light leads
to the charge separation process that causes proton translocation with generation of
