Biophysical Journal 6: 825-847 (1966)
© 1966 the Biophysical Society

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Studies of Photosynthesis Using a Pulsed Laser

I. Temperature Dependence of Cytochrome Oxidation Rate in Chromatium. Evidence for Tunneling

ABSTRACT

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 µsec at room temperature increasing to 2.3 msec at about 100°K and constant at the latter value to 35°K or below. The temperature dependence above 120°K corresponds to an activation energy of 3.3 kcal/mole; that below 100°K to less than 80 cal/mol: essentially a temperature-independent electron transport reaction. Since the slowness below 100°K indicates the presence of a barrier, the lack of activation energy is taken to mean penetration by quantum-mechanical "tunneling."

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