Abstract
1. 1. Pentachlorophenol (PCP) markedly inhibited the light-dependent formation of chlorophyll and 5-aminolevulinic acid (ALA) in a parallel fashion in the pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus. 2. 2. This indicates that the site of inhibition of chlorophyll formation occurs at or before the synthesis of ALA. The ALA-forming enzyme, 5-aminolevulinic acid synthetase, was not inactivated by PCP. The formation of ALA synthetase however, was inhibited by PCP to the same extent as ALA biosynthesis. 3. 3. PCP also inhibited total protein formation and the activity of structurally-bound photosystem II of photosynthesis. Respiration was stimulated at lower concentrations of PCP, suggesting that it has uncoupling activity. 4. 4. From our experiments we suggest that the inhibiting effect of PCP may be due to a general and far-reaching effect on metabolism, possibly by modifying membrane structure or formation.
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