DETERMINATION OF CELLULAR LEVELS OF NONPROTEIN THIOLS IN PHYTOPLANKTON AND THEIR CORRELATIONS WITH SUSCEPTIBILITY TO MERCURY¹

Abstract

We determined the intracellular contents and concentrations of cysteine and glutathione in five species of marine phytoplankton, Tetraselmis tetrathele (West) Butcher (Prasinophyceae), Porphyridium purpureum (Bory) Drew et Ross (Rhodophyceae), Pavlova sp. (Haptophyceae), Isochrysis sp. (Haptophyceae), and Pleurochrysis carterae (Braarud et Fagerl) Christensen (Haptophyceae), and examined relationships to mercury susceptibility. Intracellular contents (concentrations) of nonprotein thiols in the five species ranged from 119 to 1210 amol (0.66–12.0 mM) for cysteine, 78 to 719 amol (0.65–2.52 mM) for cystine, 31 to 677 amol (0.13–1.25 mM) for reduced glutathione (GSH), and 12 to 123 amol (0.15–0.26 mM) for oxidized glutathione (GSSG). The intracellular contents of the nonprotein thiols were not proportional to the intracellular concentrations because the cell sizes differed. Oxidation ratios of cysteine:cystine and GSH:GSSG were also wide ranging in the five species, and the higher the concentration of the reduced form of nonprotein thiols, the less they tended to be oxidized. Flow cytometric analyses with fluorescein diacetate were used to monitor the effect of HgCl2 on esterase, and the 50% effect concentrations (EC50) were compared in the five species. The EC50 after 3 h exposure to HgCl2 correlated well with the GSH concentrations but not with those of cysteine. These results indicate that the intracellular concentrations of the nonprotein thiols reflect antioxidant activity and susceptibility to heavy metals.

Analysis of glutathione endpoints for measuring copper stress in Chlamydomonas reinhardth

“…Concentrations were 26 Ϯ 2.6 and 17 Ϯ 0.7 amol/cell (0.18 Ϯ 0.02 and 0.12 Ϯ 0.01 mM) for 6 and 24 h, respectively ( Table 2). In comparison, Satoh et al [6] observed that GSSG levels in unstressed marine algae were similar among species (0.15-0.26 mM). The GSH levels also were influenced significantly by incubation time ( p Ͻ 0.05) and decreased in Cu added flasks from 6 to 24 h. Apparently, GSH was depleted faster in the detoxification process than the rate of synthesis, Cu inhibited the production of GSH, and/or the GSH pool was depleted by phytochelatin synthesis.…”

“…Trace metal toxicity is the result of various effects, including disruption of enzymes, photoinhibition, substitution of essential metals, reactive oxygen species formation, and antioxidant depletion [1][2][3][4]. Glutathione (␥-glutamylcysteinylglycine) is the most abundant nonprotein thiol in all eukaryotic cells, typically present in millimolar concentrations (ranging from about 0.1-3.3 mM glutathione in nonstressed cells) [5,6], and functions as an antioxidant to protect cells from environmental stresses. It has been shown that depletion of this thiol results in oxidative stress as well [1].…”

Impact of environmental stress on biochemical parameters of bacteria reducing chromium

“…This difference in the ability to induce the non-protein thiols among these strains might be due to variation in tolerance level to chromate. Although, there is very little information available about intracellular concentration of cysteine in living organisms, it is reported that in several species of eukaryotic algae, cysteine content ranges from 0.6 to 12 mM (Satoh et al , 2002). Cysteine concentrations of both P. aeruginosa Rb-1 and O. intermedium Rb-2 were also within this range.…”

“…Total GSH (Gamma-L-glutamyl-L-cysteninylglycine) and GSSG [Bis (gamma-Glutamyl-L-cysteinylglycine) Disulfide] were measured by the GSSG recycling method, with GSSG as the standard (Satoh et al , 2002). …”

Understanding tetrazolium reduction and the importance of substrates in measuring respiratory electron transport activity

“…For example, glutathione in marine phytoplankton ranges from 0.08 to 3.1 mM (Rijstenbil and Wijnholds, 1996) for phytoplankton, and 45.7 ± 0.92 mg/g protein for marine Decapoda (Wang et al, 2008). Cysteine in phytoplankton ranges from 0.04 to 2.23 mM, (Rijstenbil and Wijnholds, 1996;Satoh et al, 2002), and ascorbic acid ranges from 59 to 5400 μg/g dry weight (Brown and Miller, 1992;Maldonado, 2009). In our experiments we selected concentrations within these ranges.…”