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

Abstract

Pigment biosynthesis in the cyanobacterium, Anacystis nidulans, was examined in the presence of gabaculine (5-amino-1,3-cyclohexadienylcarboxylic 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. 5-Aminolevulinic acid was a principle component of the mixture, identified by thin layer chromatography. Excretion of 6-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 6-aminolevulinic acid in cyanobacteria.Recovery of cyanobacteria from iron deficiency is accompanied by a reproducible pattern of photosynthetic membrane repair. When iron is restored to a chlorotic culture, there is a 3 to 5 h lag, followed by the synthesis and insertion of Chl proteins into existing membranes (23). At later times, the assembly of new membrane becomes apparent (27). The factors which regulate the assembly of Chl proteins under these conditions are not well understood. Iron starvation reduces the synthesis of protoporphyrins, presumably by feedback inhibition due to an accumulation of protoheme (5,8,28). Since Chl is a component of several thylakoid membrane polypeptides, decreased Chl availability may play a regulatory role in Chl protein assembly.The differential effects of Chl availability and of intracellular iron during recovery from iron deficiency have previously been examined using two inhibitors of Chl biosynthesis (12). One of these, LA2, is a competitive inhibitor of ALA dehydratase (17,18), and effectively blocks protoporphyrin biosynthesis in both normal and iron-deficient cyanobacteria (1 1). The mechanism by which the second inhibitor, GAB, affects cyanobacteria is virtually unknown (12). This compound interferes with pyridoxal phosphate-linked aminotransferase activity (25,26), and inhibits Chl biosynthesis in higher plants (9,10,15,29).In this report, we have examined the effects of GAB on Our findings consist of three pertinent observations. First, GAB inhibited the accumulation of both Chl and PC. The concentration requirements for inhibition were similar to those of other systems (15,25). Second, these concentration requirements were influenced by the nutrient status of the cell. Finally, GAB induced the excretion of organic acids, a major excretion product being ALA. This suggested that GAB inhibits Chl biosynthesis in cyanobacteria at a site following ALA formation. MATERIALS AND METHODSCells of Anacystis nidulans R2 were grown in shaking culture as previously described (13). Axenic cultures were monitored microscopically and by...

The Highly Abundant Chlorophyll-Protein Complex of Iron-Deficient Synechococcus sp. PCC7942 (CP43[prime]) Is Encoded by the isiA Gene

“…Previous work suggests that Chls associated with CP43' may be used for the biosynthesis of new reaction centers following the addition of iron to iron-starved cultures (Troyan et al, 1989). These results were obtained using the compound gabaculine, which is known to inhibit Chl biosynthesis in cyanobacteria (Guikema et al, 1986). When gabaculine was added along with iron to iron-deficient cultures, normal PSII reaction center Chl-protein complexes, CP47 and CP43, were shown to accumulate, although at reduced levels.…”

Formation of the chlorophyll precursor delta-aminolevulinic acid in cyanobacteria requires aminoacylation of a tRNAGlu species

“…This drug is a potent inhibitor of yaminobutyrate aminotransferase (38) and reduces the biosynthesis of plant chlorophyll (14,23) and of tetrapyrroles in cyanobacteria (13,18). The target of gabaculin inhibition in barley chloroplasts is the GSA aminotransferase (23).…”

Discovery of a Chlorophyll Binding Protein Complex Involved in the Early Steps of Photosystem II Assembly in Synechocystis

“…Therefore, we constructed a mutant that contains the D1 and D2 proteins but lacks PSI, CP47, and CP43, together with its variant lacking Ycf39. We exposed these mutants to a short high-light treatment in the presence of the chlorophyll biosynthesis inhibitor gabaculine (Guikema et al, 1986) and simultaneously monitored the levels of the D1 protein and early chlorophyll precursors Mg-protoporphyrin and its monomethyl ester. The DPSI/CP47/CP43/Ycf39 strain showed a strong depletion of Mg protoporphyrin during 30-min exposure to high light indicating consumption of chlorophyll biosynthesis intermediates for biosynthesis of new chlorophyll while the precursors in the control strain remained stable ( Figure 6A).…”