Effects of Gabaculine on Pigment Biosynthesis in Normal and Nutrient Deficient Cells of Anacystis nidulans

Pigment biosynthesis in the cyanobacterium, Anacystis nidulans, was examined in the presence of gabaculine (5-amino-1,3-cyclohexadienyl-carboxylic acid). At 20 micromolar, this inhibitor blocked the biosynthesis of both chlorophyll and phycocyanin. Analogs of gabaculine were not effective as inhibitors of chlorophyll or phycocyanin biosynthesis. Iron- and phosphate-deficient cultures were 2- to 4-fold more sensitive to the inhibitor than were normal or nitrate-deficient cultures. Inhibition resulted in the excretion of a mixture of organic acids by the cells. delta-Aminolevulinic acid was a principle component of the mixture, identified by thin layer chromatography. Excretion of delta-aminolevulinic acid occurred following a brief lag after gabaculine addition. It remained linear for nearly 24 hours and was dependent upon illumination. However, high light inhibited excretion. Apparently, gabaculine blocks chlorophyll biosynthesis after the formation of delta-aminolevulinic acid in cyanobacteria.