GLYCOLLATE EXCRETION BY N-2-FIXING CYANOBACTERIA TREATED WITH PHOTORESPIRATORY INHIBITORS

The effects of various inhibitors of glycollate metabolism on glycollate excretion, photosynthetic CO2 assimilation and N2 fixation by cyanobacteria were examined. .alpha.-HPMS (.alpha.-hydroxy-.alpha.(2-pyridyl)-methanesulfonate) increased the rate of glycollate excretion by Anabaena cylindrica considerably, but also inhibited net CO2 photoassimilation and N2 fixation. .alpha.-HPMS inhibited glycollate dehydrogenase in A. cylindrica extracts but did not affect ribulose bisphosphate carboxylase or phosphoglycollate phosphatase activities. Diamox (5 acetamideo-1,3,5-thiadizaole-S-sulfonamide) also stimulated glycollate excretion, inhibited CO2 fixation and caused a low inhibition of N2 fixation. INH (isonicotinic acid hydrazide) enhanced glycollate excretion by A. cylindrica, suggesting the metabolism of glycollate via the glycine-serine pathway, but again inhibited CO2 fixation and N2 fixation. Glyoxylate also stimulated glycollate excretion by A. cylindrica, A. variabilis and Nostoc muscorum. The data are discussed in terms of the specificity of glycollate metabolism inhibitors in cyanobacteria and the regulation of glycollate metabolism in these organisms.