In the model of Brown & Tuszynski (2003) the assessed value is W = 0.4 eV
(6.4×10 - 20 J), the electron charge is e = 1.6 ×10 - 19 C and the hopping distance is
approximately 4nm. Thus we find that the needed electric intensity of the field is:
(106)
6.4×10-20 J
1.6×10-19C×4×10-9m
= 108V.m-1
In the framework of the same ferroelectric model Trpisova & Brown (1998)
predict that the electric fields inside cell wouldn’t have an effect on the dipolar
ordering in microtubules. The electric fields start to be effective when they
exceed intensity 104-105 V/m. The same result implying low effectiveness of the
existing electric field is presented also in another papers (Tuszynski et al., 1997b;
1998; Brown & Tuszynski, 1999). Indeed the intracellular electric field is 1-10 V/m
(Jaffe & Nuccitelli, 1977) and in vitro studies showed that if the electric field
exceeds 2x103 V/m the microtubules are destructed Stracke et al. (2001; 2002).
The energy for the electron hopping between the α- and β-tubulin could be
derived from GDP molecule hydrolysis attached to β-tubulin. GDP hydrolysis
releases approximately 0.4eV per molecule and is accompanied by a
conformational change (Audenaert et al., 1989). This change has been modeled
as resulting in a 27o angle (Melki et al., 1989) between the original line
connecting the centers of the α- and β-monomers and the new centre-to-centre
line. These two conformational states and their associated dipole moments have
been proposed as the basis for a binary system for information storage and
manipulation (Hameroff & Watt 1982; Hameroff, 1987; 1998a, 1998b; Hameroff
et al., 1988; 1992; Smith et al., 1984; Rasmussen et al., 1990; Mavromatos et al.,
2002; Mershin et al., 1999; Mershin, 2003; Schuessler et al., 2003). However this
model is flawed because the associated conformational change α <-> β is not
biologically useful for computation - leads to microtubular destabilization (Tran et
al., 1997) and indeed is linked to assembly <-> disassembly i.e. with microtubule
construction <-> destruction.
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