Reply to Criticisms of a Quantum-Mechanical Muscle Model

Abstract

THE fundamental idea in a highly speculative new kind of muscle model¹ was that a bond vibration is first produced by an exothermic chemical reaction, the energy is transferred resonantly to an electronic excited state of identical frequency, then trapped in an excimer state formed between two such electronic oscillators and finally converted into external work as the two oscillators approach each other. The first part of Naqvi's criticism² was that the experiment I quoted as an example of energy trapping in excimers was mistaken. This I concede; clearly the pyrene experiments can no longer be used to show that excimer fluorescence is dipole-forbidden. The accepted theory clearly predicts, however, that, in special conditions, the excimer state may yet be long lived. In its longer version³ my muscle model already has a design feature which enables Naqvi's criticism to be overcome. If the oscillator was indeed first excited to a singlet state and only later diffused into interaction distance with another oscillator in the ground state then, as Naqvi argues, the triplet state would be at a lower energy and decay into it would be difficult to avoid. My suggestion³ was, however, that the energy of the bond vibration produced on ATP hydrolysis is less than that of the excited state of an isolated oscillator, so that only when the two oscillators are close enough to perturb each other sufficiently do they resonate with the bond vibration and then become excited. This feature was introduced, first, to protect the postulated bond vibration (by allowing it to be buried in a protein and yet to interact with the environment in this way) and, second, to ensure that only the anti-symmetric attractive excimer state is produced on excitation. I now suggest a third function: to ensure that the excimer only becomes excited when its energy is already below that of the triplet state. In this case decay into the triplet state would be prevented, and the fluorescence would become fully dipole-forbidden.