ULTIMATE COMPUTING - Quantum Consciousness Studies

86 Cytoskeleton/Cytocomputer
lattices with a “leftward” tilt and several helical patterns may be discerned in the
relations among dimers. The crystal-like symmetry packing of tubulin in
microtubules has been evaluated by Djuro Koruga (1986) of the Molecular
Machines Research Unit at the University of Belgrade in Yugoslavia (Chapter 8).
MT from different life forms have marked similarities, but subtle differences.
Comparison of MT from nerve cells of earthworms and mammals shows that the
more primitive worm MT are more variable in geometric structure with MT
ranging from 9 to 11 protofilaments, whereas mammalian MT generally have 13.
Tubulins from among different species including mammals and plants bind to
common antibodies and tubulins from different species may coassemble into
hybrid MT. Despite these common traits, the diversity of tubulin gene expression
has proved far greater than imagined years ago. Analysis of tubulin by amino acid
sequencing and advanced electrophoretic techniques have shown that multiple,
different alpha and beta tubulins exist concurrently, with the greatest diversity
shown by beta tubulin. For example, Lee (1986) and colleagues at St. Louis
University have shown that as many as 11 different tubulin forms exist in rat
thyroid microtubules and 17 different forms exist in rat brain microtubules. Thus
alpha and beta tubulin are families of “isozymes,” each of which may have
specific functions or binding of microtubule associated proteins (MAPs). Another
tubulin variable, detyrosination, occurs in the cytoplasm subsequent to DNA
transcription. Detyrosination is the removal of the terminal amino acid, tyrosine,
from the polypeptide chain which comprises beta tubulin. Removal of tyrosine
exposes an acidic amino acid, glutamate. Local factors in the cytoplasm
independent of genetic programming determine whether or not individual tubulin
subunits are “tyrosinated” or “glutamated.” Marc DeBrabander (1986) and
collaborators at Janssen Pharmaceutica in Belgium have been able to identify
specific tubulin subunits within assembled microtubules which are either
tyrosinated or glutamated. Their elegant studies show heterogeneous patterns of
tyrosinated and glutamated tubulin which could indicate an information
representation coupled to specific MT functions by the action of MAPs (Figure
5.5).
Figure 5.5: Microtubule double labeled with immunogold tubulin antibody. Large
circles, 10 nanometer gold particles, label glutamated tubulin; small circles, 5
nanometer gold particles, label tyrosinated tubulin. With permission from Geuens
et al (1986), courtesy of Marc DeBrabander and Janssen Pharmaceutica
Research Laboratories.
Since early electron microscopy studies, microtubules have been invariably
described as being surrounded by a “clear zone” which gives the impression of a
“halo” around them when they are viewed in cross section. A 5–10 nanometer
distance from the surface of MT is free of cytoplasmic ground substance or any
other material normally seen elsewhere throughout the cell. These clear spaces
were initially thought to be electron microscopic artifacts, or layerings of less