QUANTUM REQUIREMENT OF THE LIGHT-INDUCED PROTON UPTAKE BY SPINACH CHLOROPLASTS

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Abstract
The quantum requirement for light-induced H+ uptake by spinach chloroplasts has been determined as a function of light intensity and 3 electron transport cofactors. A minimum quantum requirement (extrapolated to zero light intensity) of 0. 2 quantum absorbed per H+ transported was found for both 700- and 710-m[mu] illumination, and 0. 4 quantum per H+ for 685-m[mu] light. A comparison of H+ uptake to electron transport at wavelengths from 650 to 710 m[mu] shows a fairly constant ratio of about 5 H+ per electron over this range. The data are discussed in reference to the current concepts of energy-linked ion transport in chloroplasts.