title: The feasibility of coherent energy transfer in microtubules.
abstract: It was once purported that biological systems were far too 'warm and wet' to support quantum phenomena mainly owing to thermal effects disrupting quantum coherence. However, recent experimental results and theoretical analyses have shown that thermal energy may assist, rather than disrupt, quantum coherent transport, especially in the 'dry' hydrophobic interiors of biomolecules. Specifically, evidence has been accumulating for the necessary involvement of quantum coherent energy transfer between uniquely arranged chromophores in light harvesting photosynthetic complexes. The 'tubulin' subunit proteins, which comprise microtubules, also possess a distinct architecture of chromophores, namely aromatic amino acids, including tryptophan. The geometry and dipolar properties of these aromatics are similar to those found in photosynthetic units indicating that tubulin may support coherent energy transfer. Tubulin aggregated into microtubule geometric lattices may support such energy transfer, which could be important for biological signalling and communication essential to living processes. Here, we perform a computational investigation of energy transfer between chromophoric amino acids in tubulin via dipole excitations coupled to the surrounding thermal environment. We present the spatial structure and energetic properties of the tryptophan residues in the microtubule constituent protein tubulin. Plausibility arguments for the conditions favouring a quantum mechanism of signal propagation along a microtubule are provided. Overall, we find that coherent energy transfer in tubulin and microtubules is biologically feasible.
authors.affiliation: Center for Psychological Studies, Graduate School of Computer and Information Sciences, and College of Osteopathic Medicine, Nova Southeastern University, Ft Lauderdale, FL 33328, USA Institute for Neuro-Immune Medicine, Nova Southeastern University, Ft Lauderdale, FL 33328, USA tcraddock@nova.edu.
authors.forename: Travis John Adrian
authors.initials: TJ
authors.lastname: Craddock
authors.affiliation: Department of Oncology, University of Alberta, Cross Cancer Institute, Edmonton, Alberta, Canada T6G 1Z2.
authors.forename: Douglas
authors.initials: D
authors.lastname: Friesen
authors.affiliation: Department of Oncology, University of Alberta, Cross Cancer Institute, Edmonton, Alberta, Canada T6G 1Z2.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Mane
authors.affiliation: Departments of Anesthesiology and Psychology, Center for Consciousness Studies, The University of Arizona Health Sciences Center, Tucson, AZ 210202, USA.
authors.forename: Stuart
authors.initials: S
authors.lastname: Hameroff
authors.affiliation: Department of Oncology, University of Alberta, Cross Cancer Institute, Edmonton, Alberta, Canada T6G 1Z2 Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Tuszynski
mesh_terms: D003198:Computer Simulation; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D014404:Tubulin
keywords: energy transfer; microtubule; optical spectra; quantum biology; structure-based simulation