Cytoplasmic Solid State

Molecules such as proteins and RNA are heterogeneously distributed throughout cytoplasm and passively flow at rates below that expected for normal diffusion. Actively transported molecules such as those carried by axoplasmic transport travel at velocities far in excess of diffusion. Initially, the slow diffusion of biomolecules which are not actively transported was explained on the basis of cytomatrix barriers and channels. However, Gershon, Porter and Trus (1985) studied molecular diffusion through cytoplasm and came to a different conclusion. They found that the cytoskeleton/cytomatrix/MTL comprised from 16 to 21 percent of cytoplasmic volume, and that the cytoskeleton/cytomatrix/MTL surface area was from 69,000 to 91,000 square microns per cell (69 to 91 billion square nanometers). Their data has been interpreted to suggest that the cell "solid state" (cytoskeleton/cytomatrix/MTL) is not a barrier to diffusion since the aqueous phase occupies 4/5 of cell volume. They conclude that proteins and other molecules are dynamically bound to the solid state, accounting for the slow diffusion (Figure 5.21).

Biologist James Clegg (1981) has discussed how the binding of "soluble" enzymes to the solid state could account for the efficiency of various enzymatic processes. A sequence of enzymes in a complex biochemical pathway is much more efficient if physically arranged so that a cascade of reaction products occurs. If the product of one enzyme is the precursor for its neighbor enzyme, transfer time is minimized and the reactions are usefully facilitated. This also allows the possibility of dynamic regulation of these enzymes by the solid state structures. Clegg has also accrued evidence regarding the role of water within cytoplasm, particularly surrounding solid state structures. Using neutron diffraction and other techniques, Clegg has found that water adjacent to the cytomatrix is "ordered," that is aligned with polar bonds on the protein surfaces. Thus a layer of ordered water extends at least 3 nanometers from the billions of square nanometers of solid state surface area within each cell. This ordered water may be coupled by dipole oscillation to dynamics of the solid state, inhibit the thermal dissipation of protein oscillation energy from within the solid state, and shield calcium and other ions from random solid state interactions. Clegg also suggests that additional layers of slightly less ordered water ("vicinal water") extending further from the solid state would limit true "aqueous" water within cells to narrow cellular "sewage channels."

Figure 5.21: "Soluble" intracellular enzymes (circles) governed by the microtrabecular lattice (MTL: solid dark) and bordering region of ordered and vicinal water (within thin line). The dark circle is part of a cross sectional view. Clegg (1981) has proposed that dynamic activity within the MTL can regulate the enzymatic activity. By Paul Jablonka.

Figure 5.21: "Soluble" intracellular enzymes (circles) governed by the microtrabecular lattice (MTL: solid dark) and bordering region of ordered and vicinal water (within thin line). The dark circle is part of a cross sectional view. Clegg (1981) has proposed that dynamic activity within the MTL can regulate the enzymatic activity. By Paul Jablonka.

Is the MTL/cytomatrix the final microfrontier of biological organization? Current imaging techniques would not reveal smaller levels of organization, just as it took advances in electron microscopy to discover first the MT cytoskeleton and then later the MTL. Perhaps smaller, more intricate networks ranging down to the level of single peptide filaments might be present. With layers of ordered water and charged ions, such a solid state "infoplasm" could occupy nearly the entire volume of biological material.

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