Studies of photosynthesis using a pulsed laser. I. Temperature dependence of cytochrome oxidation rate in chromatium. Evidence for tunneling

Biophys J. 1966 Nov;6(6):825-47. doi: 10.1016/s0006-3495(66)86698-5.


The rate of oxidation of cytochrome following absorption of a short pulse of light from a ruby laser in the photosynthetic bacterium Chromatium has been measured spectrophotometrically. The half-time is about 2 musec at room temperature increasing to 2.3 msec at about 100 degrees K and constant at the latter value to 35 degrees K or below. The temperature dependence above 120 degrees K corresponds to an activation energy of 3.3 kcal/mole; that below 100 degrees K to less than 80 cal/mol: essentially a temperature-independent electron transport reaction. Since the slowness below 100 degrees K indicates the presence of a barrier, the lack of activation energy is taken to mean penetration by quantum-mechanical "tunneling."

MeSH terms

  • Chromatium / metabolism*
  • Cytochromes / metabolism*
  • Lasers*
  • Light
  • Oxidation-Reduction
  • Photosynthesis*
  • Spectrophotometry
  • Thermodynamics


  • Cytochromes