Regulation of isocitrate lyase from autotrophic and photoheterotrophic cultures of Gloeomonas sp.

Abstract

Isocitrate lyase (EC. 4.1.3.1) has been partially purified from extracts of the unicellular green alga Gloeomonas sp. grown either photoautotrophically in CO2 or photoheterotrophically with acetate resulting in a 50-fold increase in specific activity. Enzyme preparations from both cultures were eluted from DEAE-cellulose columns at almost the same position. The enzymes showed classical Michaelis kinetics with Km values of 1.14 and 1.4 mM and responded in a similar manner to metabolites. Glycol-late, 3-phosphoglycerate, ribulose diphosphate, α-ketoglutarate, succinate, malate, fumarate, and ADP inhibited the enzyme at concentrations of 10 mM. Inhibition by oxaloacetate occurred at 1 mM. Succinyl-CoA (1 mM) activated the enzyme to 155% of the control. These results are discussed in relation to the autotrophic and photoheterotrophic mode of nutrition in algae.

Isocitrate Lyase in Green Leaves

“…The enzyme has shown an apparent Km of 0.1 mm at pH 7.4 in phosphate buffer. The enzyme is susceptible to end product inhibition by succinate (Table V) as well as inhibition by oxaloacetate, DL-malate, glycolate, and 3-phosphoglycerate at 10 mm in a manner similar to that reported for algal enzyme (7). It also showed an unusual activation by ribulose-1, 5-diP.…”

“…Harrop and Kornberg (12) suggested that the presence of isocitrate lyase in autotrophic green algae would not necessarily implicate the operation of glyoxylate cycle to replenish the C4 acids as in algae or bacteria grown on acetate (14), since these acids could arise by the /8-carboxylation of phosphoenolpyruvate. This was supported further by the reports of Foo et al (7) and Badour and Waygood (2).…”

“…The enzyme in intact green leaves may be operating as in green algae to provide succinate for succinyl-CoA formation, if the latter were not produced via a-ketoglutarate dehydrogenase, as suggested by Pearce et al (21,22) and Foo et al (7). Alternately, the glyoxylate may undergo condensation and decarboxylation with a-ketoglutarate via glyoxylatea-ketoglutarate carboligase shown to be present in higher plants (6).…”

“…Isocitrate has been demonstrated in crude extracts of various unicellular algae when forced to grow on acetate as the sole carbon source (10,11). However, substantial activity has been observed in photoautotrophically grown algae with CO2 as the sole carbon source (2,3,7,12,27). Harrop and Kornberg (12) suggested that the presence of isocitrate lyase in autotrophic green algae would not necessarily implicate the operation of glyoxylate cycle to replenish the C4 acids as in algae or bacteria grown on acetate (14), since these acids could arise by the /8-carboxylation of phosphoenolpyruvate.…”

Isocitratlyase von Candida guilliermondii, Stamm H17. II. Regelung durch ausgewählte Intermediate des Tricarbonsäurezyklus und Hexoseabbaus

“…1). (Foo et al 1971). I n der Zelle setzt ein gesteigerter ATP-Spiegel (neben der Substratphosphorylierung) eine aktive terminale Oxydation und damit gekoppelt einen hohen Reduktionsgrad der Gesamtheit der Cosubstrate NADund in entsprechendem AusmaB -NADP voraus.…”