ULTIMATE COMPUTING - Quantum Consciousness Studies

Cytoskeleton/Cytocomputer 117
through a series of serpentine maneuvers. Allen and colleagues concluded that the
forces observed in their slithering free MT as well as in axoplasmic transport and
ciliary bending are due to “force generating enzymes” directly attached to MT.
Dynein, which functions to cause binding in cilia and flagella, is one MT force
generating enzyme and kinesin is another motor for organelle transport along
microtubules. Latex beads coated with kinesin translocate along microtubules
similar to organelles, although at a slower velocity. Purifled kinesin can increase
the frequency of axoplasmic organelle movement along purified MT.
Allen and colleagues proposed the “backstroke hypothesis” which states that
the force generating enzyme (dynein or kinesin) makes an elliptical stroke which
imparts some force in both directions. Allen’s dynein backstroke model is capable
of carrying vesicles in opposite directions simultaneously through sufficiently
separated pathways so that they seldom collide. Further, the motion generated can
be continuous, not interrupted by cycles of attachment and detachment. The
mechanical cycle of each sidearm includes a radial stroke that moves vesicles in
the anterograde direction toward the microtubule plus end. This part of the cycle
also causes isolated MT to glide “retrograde.” The return stroke is tangential to
the MT surface and transports the larger organelles in a retrograde pathway, and
propels gliding MT toward their . “anterograde” plus end.
The mechanisms by which the force generating protein arms may use ATP
energy to contract will be discussed in Chapter 6. Even less well understood is the
signaling and communication which orchestrates contractile activities of rows of
arms spatially arrayed on MT lattices. Collective communication among MT
lattice subunits (solitons, coherent excitations, lattice vibrations) could explain
this orchestration.
The backstroke model is currently favored more than another model:
microstreams. Shimizu and Haken (1983) had proposed a dynamic cooperativity
of cytoskeletal elements which generated hydrodynamic microstreams conveying
cellular materials. They specifically focused on actin-myosin interactions to
generate these microstreams. New techniques such as Nanovideo Microscopy
developed by Marc DeBrabander and colleagues (1986) at Janssen Pharmaceutica
Research Laboratories in Belgium show direct tracking of immunolabeled
particles along MT, questioning the significance of microstreams. Particles are
seen to travel in opposite directions along the same MT, passing each other like
two railroad trains on adjacent tracks. Microstreaming does not appear dominant
in axoplasmic transport, but could be important in other phenomena. The primary
site of coordinated transport and its complex orchestration appears to rest solely
in the province of MT.