Researchers observed that ESR signals from insoluble liver protein were strong, while ESR signals from soluble proteins were weak. This indicated that membrane proteins, including lipid-associated proteins and tubulin, which are part of the insoluble fraction, may function as semiconductors whereas proteins in the soluble fraction cannot be expected to be semiconductors.
Figure 1 shows the prominent ESR spectra observed from the insoluble fraction of healthy liver tissue.
In contrast, little signal was observed for the soluble fraction. Pohl and Szent-Gyorgyi explained the different ESR spectra as being associated with "vegetative" or "work" proteins. Vegetative or soluble proteins of liver lack an ESR signal because they are likely to have closed shell orbitals, whereas the work or insoluble proteins have unpaired electrons which confer electroconductive properties, that essentially allow the proteins to do work. Pohl and Szent-Gyorgyi wrote:
"According to the concepts developed in this laboratory, the simple "vegetative" functions are still performed by soluble molecules with closed shells of electrons, while the more complex "animal" functions which produce work, W, and involve energy transformations are performed by the insoluble structures, characterized by their electronic disbalance." (H.A. Pohl, 1977)Microtubules, which are composed of tubulin protein, are associated with "work" functions in the cell, and have a long history of work at separating the chromosomes of dividing cells.
Whereas DNA and proteins are held together by covalent linkages, microtubules are thought to be held together by weak non-covalent interactions, which means that their assembly and disassembly is controlled without covalent bonds being formed or broken. As compared with covalent bonds, less energy is needed to break or form non-covalent interactions, and typically the microtubule switches between "catastrophe" - a change to rapid shrinkage - and "rescue" - a change to rapid growth a few times per minute, as microtubules maintain a dynamic equilibrium. Nearby dipoles and electromagnetic fields have an essential role initiating the assembly and disassembly of tubulin monomers and affecting microtubule dynamics.
Tubulin protein is very unique and different when compared with the soluble proteins of the cell, because it is capable of undergoing transformation because of its access to "free" electrons. The work by Szent-Gyorgyi and Pohl suggested that proteins in the soluble fraction of liver are incapable of such transformations. Like many organic molecules, soluble proteins may have even numbers of electrons that fill the available energy levels in pairs.
In a lattice of multiple tubulin proteins, numerous molecular orbitals overlap, forming what is known as a conduction band, along which unpaired electrons travel. In the cell where biopolymers are intimate contact with each other, it is quite conceivable that unpaired electron migration may take place over large distances involving a number of aggregated tubulin. Microtubules can be aligned by electric currents, as shown below.
In the absence of electric fields, microtubules translocate in random directions, however, as soon as the electric field is applied, microtubules start to turn toward the anode and align with the direction of electric fields. After 30 seconds, nearly all the microtubules are translocating roughly parallel to the electric field toward the anode.
Clearly, there is an interplay between the assembly of the cytoskeleton and the electrical fields of the body. Bioelectric fields of the body (e.g. EEG) certainly interact with cytoskeletal proteins in the radical state (e.g. tubulin proteins that give rise to a large ESR signal), whereas the insoluble "vegetative" proteins with closed shell orbitals may be more resistant to these field currents.
References
Pohl, H. A., P.R. Gascoyne and A. Szent-Gyorgyi 1977. Electron spin resonance absorption of tissue constituents. Proc. Natl. Acad. Sci. U. S. A. 74, 1558-1560. DOI:10.1073/pnas.74.4.1558
Kim, T., M.T. Kao, E.F. Hasselbrink and E. Meyhofer 2007. Active alignment of microtubules with electric fields. Nano Lett. 7, 211-217. DOI:10.1021/nl061474k
