[Photochemical reaction of chlorophyll a and pheophytin a with low concentrations of hydroquinone].

It has been shown that when illuminating chlorophyll a solution (approximately 10(-5) M) in ethanol containing small concentrations of hydroquinone at pH higher than 7, a markable negative photopotential (-PhP) is initiated. Similar picture is also observed both in the presence of 2 . 10(-5) M parabenzoquinone and when using pheophytin a instead of chlorophyll. The data obtained are in favour of the idea that when illuminating the solutions of these pigments in ethanol containing pure p-benzoquinone at pH higher than the definite value, PhP initiation is conditioned by photochemical reaction of pigments with equilibrium amounts of hydroquinones or semiquinone always present in quinone solutions.