The presence of glycollate oxidase and dehydrogenase in Dunaliella primolecta

Abstract

Homogenates of Dunaliella primolecta, D. salina and D. tertiolecta were assayed for glycollate oxidase and glycollate dehydrogenase. Both D. primolecta and D. salina but not D. tertiolecta showed substantial glycollate-dependent O2-uptake which is characteristic of glycollate oxidase. L-Lactate was an alternative substrate and both glycollate- and L-lactate-dependent O2 uptake were insensitive to 2 mM cyanide. Glycollate dehydrogenase, measured by following the glycollate-dependent reduction of 2,6-dichlorophenolindophenol under aerobic conditions, was present in D. primolecta, D. salina and D. tertiolecta. In the presence of glycollate and D-lactate, rates were additive so both glycollate and D-lactate dehydrogenases are present in the homogenates. Glycollate and D-lactate oxidation were both inhibited by 2 mM cyanide. Organelles released from phototrophically grown cells of D. primolecta were separated by isopycnic centrifugation on sucrose gradients. Glycollate oxidase was present in the peroxisome fraction at an equilibrium density of 1.25 g/cm(3), while the major peak of glycollate dehydrogenase activity was in the mitochondrial fraction at an equilibirium density of 1.22 g/cm(3).

Localization of glycolate dehydrogenase in two species of Dunaliella

“…Also, hydroxypyruvate reductase was identified only in the mitochondria and not in the peroxisomes. According to our data the peroxisomes of D. primolecta are altogether not of the leaf-type as suggested by the results of Nimer et al (1990), but of the Eremosphaeratype which is characteristic of chlorophycean algae (Stabenau , 1992(Stabenau , 1992a. In accordance with this fact the distribution pattern of hydroxyacyl-CoA dehydrogenase (Fig.…”

“…Therefore, previously published data indicating the presence of glycolate oxi- 0-0~0 I~ 9 .i"I" \ for only 45 min, therefore the peroxisomes did not reach their specific density. Enzyme activities: 10 units correspond to the following activities per ml fraction: cytochrome C oxidase, 200 pkat; malate dehydrogenase, 250 nkat; glycolate dehydrogenase, 20 pkat; hydroxypyruvate reductase, 600 pkat; hydroxyacyl-CoA dehydrogenase, 300 pkat; uricase, 100 pkat dase in D. salina (Nimer et al 1990) could not be confirmed. As with D. primolecta, glycolate dehydrogenase along with hydroxypyruvate reductase is located exclusively in the mitochondria, while the peroxisomes appear to be of the Eremosphaera-type.…”

“…Recently, it was reported that two species of Dunaliella (D. salina and D. primolecta) possess glycolate oxidase along with glycolate dehydrogenase (Sallal et al 1987;Nimer et al 1990;Merrett 1992), while in D. tertiolecta glycolate dehydrogenase was found to be the only glycolate-oxidizing enzyme (Frederick et al 1973;Nimer et al 1990). Since Dunaliella is a flagellate of the class Chlorophyceae, the presence of glycolate oxidase would be very unusual and not in accordance with the observations made hitherto.…”

Identification and Characterization of Glycolate Oxidase and Related Enzymes from the Endocyanotic Alga Cyanophora paradoxa and from Pea Leaves

“…This means that such isozymes, if present in Cyanophora, would produce normal and identical Michaelis-Menten kinetics with glycolate as a varied substrate but different kinetics with oxygen as varied substrate. To date, however, there have been only two reports that two glycolate-oxidizing enzymes, GO and GD, would occur together in the same organism (25,26). Thus, it is more probable that Cyanophora has only one enzyme that can bind oxygen cooperatively.…”

Core metabolism plasticity in phytoplankton: Response of Dunaliella tertiolecta to oil exposure

“…The observed increasing cellular ROS levels during oil exposure under increasing inhibition of photorespiration confirms anti-oxidation as one of the physiological functions. In addition, several studies have shown that the glycolate secreted by Dunaliella tertiolecta and other species of Dunaliella is then reassimilated in ROLE OF CORE METABOLISM DURING OIL EXPOSURE the cells (Nimer et al 1990, Sciandra et al 1997, Leboulanger et al 1998, through the action of glycolate oxidase or glycolate dehydrogenase into the glyoxlate pathway (Nimer et al 1990, Stabenau et al 1993. Moroney et al (2013) suggested photorespiration "limits" the loss of carbon by oxygenation by RuBisCO, as only one molecule of CO 2 is lost after accounting for glycolate oxidase or glycolate dehydrogenase activity.…”