[Spectroscopic study of "hole burning" of the initial photoprocesses in photosystem I of mutant strain Chlamydomonas reinhardii 516-3a enriched with P700 reaction centers].

The effect of "hole burning" in absorption spectrum upon monochromatic illumination at 4.2 degrees K has been investigated on the Chlamydomonas reinhardii mutant strain 516-3a which possesses the chlorophyll a/P700 ratio of about 25. This effect has been earlier discovered for the wild type strain of Chlorella. In the strain 516-3a two types of holes differing in width and in shape have been observed. For their assignment the maximal (saturated) holewidth has been studied as a function of the burning wavelength. It has been shown that for the holes of one type photooxidation of P700 is responsible. The other type of holes is caused by electrochromic transition shift of another component of the reaction centre with the absorption maximum at 693 nm. Using measured holewidths it has been estimated that the lifetime of P700 excited state is not less than 50 ps and that the excited state lifetime of the component responsible for the other type of holes is 8.6 ps. The latter, in assumption that it is limited by energy transfer between two components under consideration, gives a distance of 20 A between them. Possible reasons of disagreement between obtained P700* lifetime and considerably shorter times attributed earlier to the primary electron phototransfer in photosystem I on the basis of picosecond studies are discussed.