Effects of Aminooxyacetate and Aminoacetonitrile on Glycolate and Ammonia Release by the Cyanobacterium Anabaena cylindrica

Abstract

Aminooxyacetate and aminoacetonitrile cause increased excretion of glycolate by the cyanobacterium Anabaena cylindrica. Both compounds also reduce NH4-N release induced by methionine sulfoximine in nonnitrogen-fixing cultures. Changes in amino acid pool sizes together with changes in activities of some enzymes related to glycolate metabolism show that glyoxylate to glycine conversion and glycine to serine conversion are inhibited by aminooxyacetate and aminoacetonitrile, respectively. The results also verify that photorespiratory glycolate metabolism via amination of glyoxylate is operative in A. cylindrica.We have recently reported on the stimulation of glycolate excretion by INH2 in cultures of the cyanobacterium Anabaena cylindrica (4). INH inhibits the conversion of glycine to serine in the glycolate pathway of higher plants and eukaryotic algae (27). Evidence has also been presented for the photorespiratory production of ammonia by A. cylindrica (3). As with some green algae (13,23) Medium and Cultivation. Cells were grown in pure culture in either NH4Cl-supplemented (N+) or N-free (N-) BG 11 medium (26) and sparged continuously with sterile air. Cultivation and cell harvesting from N+ and N-media were carried out as detailed earlier (1, 3, 4). The N+-grown cultures were used in experiments on the release of ammonium and amino acid pool sizes, while N-grown cells were used in the remainder of the experiments. Solutions ofall inhibitors were adjusted to pH 7.5 before addition to the medium.Glycolate Excretion. The procedure given earlier (4) was used and excreted glycolate assayed according to Calkins (6). The cultures were grown on air before use and then sparged with 100% 02 from the beginning of the excretion experiments. A photon fluence rate of 200 Mumol. m2 . s' at the surface of the vessels was used during excretion assays, provided by white fluorescent tubes.Release of NH4-N. MSX (0.2 mM)-induced release of NH4-N to the medium was determined as detailed earlier (3), using the phenol hypochlorite method of Chaney and Marbach (7). Cultures were pretreated only with AOA, AAN, and INH as they all, as such, interfere with the colorimetric assay by producing a blue color similar to that of indophenol blue. Cells were centrifuged after exposure to the inhibitors, carefully washed, and resuspended in fresh N-free medium containing 0.2 mM MSX (time zero). The release of NH4-N to the medium was then determined at the time intervals given in Tables III and IV

Glyoxylate Induced Changes in the Carbon and Nitrogen Metabolism of the Cyanobacterium Anabaena cylindrica

“…In Anabaena the excretion of glyoxylate was negligible, however, and glyoxylate had no effect on the RuBP carboxylase activity. The data presented herein stress the validity of earlier observations which show that glyoxylate primarily acts within the photorespiratory process in cyanobacteria (3,4,6), a process residing exclusively in the vegetative cells of Anabaena (11), and that glyoxylate may be metabolized via glycine to serine as in higher plants (5,7). In particular, the 20-fold increase in the glycine pool supports such a statement.…”

“…Na glycolate given at 2, 5, 10, and 20 mm caused some stimulation in both N2 and CO2 fixation, but glyoxylate given at equimolar concentrations caused several-fold larger effects (3,4). Moreover, glycolate was without effect on the MSX-induced release of NH4+, while glyoxylate slightly stimulated NH4' release (5 (5,7,16). The fourth route is part of the glyoxylate by-pass and occurs mainly in the dark (10).…”

“…Cells were harvested, washed, disrupted twice in a French Pressure Cell (110 MPa) and lyophilized. Amino acid pools and ammonia were analyzed using an automatic amino acid analyzer as described earlier (7). Norleucine was added as internal standard.…”

Assessment of salinity-induced photorespiratory glycolate metabolism in Anabaena sp. PCC 7120

“…The increase in glyceric acid content results from enhanced respiration and glycolate metabolism in the salt-stressed cells, as reported previously . Although cyanobacteria have four different routes to metabolize glyoxylate, it is primarily metabolized through the photorespiratory process as in higher plants (Bergman, 1986;Bergman et al, 1985). Hyperaccumulation of glycolic and glyoxylic acid, as well as the observable increase in glycine and serine content in salt-stressed cells, supports the hypothesis of a photorespiratory pathway being present in Anabaena PCC 7120.…”

Inhibition of Spinach Leaf NADPH(NADH)-Glyoxylate Reductase by Acetohydroxamate, Aminooxyacetate, and Glycidate

“…Both GHA and AOA (as well as aminoacetonitrile which had no effect on GR activity) are structurally related to glycine and have been shown to inhibit glycine oxidation (2,7,9,11,17,18,23,28). AOA has also been reported to inhibit glyoxylatedependent aminotransferases (2,10,11,23,26) and an NADPHdependent activity of GR from Chiamydomonas (K, of 1 mM 126]). All of these inhibitors are water soluble, have low mol wt and are easily taken up by leaves or isolated organelles.…”