The influence of pentachlorophenol on the biosynthesis of 5-aminolevulinic acid and chlorophyll

Pentachlorophenol induced physiological-biochemical changes in Chlorella pyrenoidosa culture

Present study investigated physiological and biochemical changes in a green alga culture (Chlorella pyrenoidosa) upon exposure to varied concentrations of pentachlorophenol (PCP) (0, 0.4 mgL(-1), 2.5 mgL(-1) and 10 mgL(-1)). The results revealed that with the increase of PCP concentration, a decrease of the algal biomass, levels of photosynthetic pigments (chlorophyll a, b and carotenoid), soluble protein and an increase of nitrate reductase (NR) activity were observed. This suggests that the PCP may serve as an uncoupler, causing low ATP level within the algal cells and led most of the NR molecules to be in the dephosphoration state (i.e. active from). Moreover, it shows that photosynthetic pigments especially carotenoid were more sensitive indicators to indicate PCP toxicity as compared to the other parameters.

Pentachlorophenol-induced change of zeta-potential and gel-to-fluid transition temperature in model lecithin membranes

We have determined zeta-potentials for dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) membranes by measuring the electrophoretic mobility of multilayered vesicles and the temperatures of the gel-to-ripple-to-fluid phase transitions of sonicated vesicles by a photometric method. Some conclusions are: (1) The zeta-potentials of DMPC and DPPC vesicles become negative due to adsorption of ionized pentachlorophenol (PCP), (2) their magnitude changes, step-like, on gel-to-fluid transition and (3) the temperature of the step-like change in zeta-potential decreases with an increase in PCP concentration. (4) PCP exhibits a large effect on membrane structure: It induces an isothermal phase change from the ordered to disordered state, which is enhanced by monovalent salt in the aqueous phase. (5) Both ionized and unionized PCP decrease the melting phase transition temperature and abolish the pretransition, (6) the unionized species increases the melting transition width and (7) the ionized species is more potent in abolishing the pretransition. (8) The shorter chain lipid (DMPC) is more sensitive to the presence of PCP; the maximum decrease in delta Tt is 13 K (DMPC) and 7 K (DPPC) in the presence of ionized PCP. We have shown experimentally, by comparing the delta Tt from photometric studies with the density of adsorbed PCP derived from zeta-potential isotherms, that (9) the shift of the melting phase transition temperature increases linearly with the density of adsorbed PCP. (10) In contrast to membranes made of negatively charged lipids, the transition temperature of DMPC and DPPC membranes in the presence of PCP further decreases in the presence of monovalent salt. The salt effect is due to screening of the membrane surface leading to enhanced adsorption of ionized PCP and a depression in transition temperature. (11) It is shown that both the adsorption and the changes of gel-to-fluid phase transition temperature can be described in terms of the Langmuir-Stern-Grahame model and (12) proposed that future studies of membrane toxicity of PCP should be focused on its pH dependence.

Adsorption of ionized and neutral pentachlorophenol to phosphatidylcholine membranes

We have studied adsorption of pentachlorophenol (PCP) to phosphatidylcholine (PC) membranes by measuring the electrophoretic mobility of multilayered lipid vesicles in PCP solutions. PC vesicles become negatively charged due to the adsorption of ionized PCP, and we have found that their zeta potential depends upon the ionic strength and pH of the aqueous suspension. We have shown that the experimental results can be adequately accounted for in terms of a two-component Langmuir-Stern-Grahame adsorption model assuming that the 'PCP adsorption sites' are occupied either by the neutral (HA) or the ionized (A-) species. The characteristics of adsorption isotherms of the PCP - PC membrane are as follows: the association constants are KA = 55,000 dm3/mol, KHA = 279,000 dm3/mol; 4.3 PC molecules make up each PCP adsorption site at saturation; the linear partition coefficients are beta HA = (15.5 +/- 0.7) x 10(-5) m and beta A = (3.0 +/- 0.3) x 10(-5) m. The properties of PCP adsorption isotherms for PC membranes predict an increased pKa value of membrane-bound PCP, which has been observed in related studies.

Dielectric properties of adsorption/ionization site of pentachlorophenol in lipid membranes

The results of three complementary studies focused on characterization of the local environment of the common pesticide pentachlorophenol (PCP) adsorbed to phosphatidylcholine (PC) and phosphatidylglycerol (PG) membranes are reported. The effect of cholesterol (Chol) was examined. These studies included: Measurements of solvatochromic shifts of the ultraviolet absorption spectra of PCP in membranes and in polar non-hydrogen-bonding (a red shift) and hydrogen-bonding (a blue shift) solvents. Pi-pi transition energies were analyzed in terms of the dielectric cavity models of Onsager, Block-Walker, which includes dielectric saturation, and a soft dipole model of Suppan, which accounts for PCP's polarizability. The estimates of dielectric constant of the PCP adsorption site yielded 8.1-8.7 for the PC and 16.8-20.1 for PG membranes. Solvatochromic effects indicate hydrogen bonding between the membrane-bound ionized PCP molecule and water, which is enhanced by the presence of cholesterol. Determinations of the pKa of PCP adsorbed to PC, PG, PC/Chol, PG/Chol membranes and dissolved in dioxane-water solutions of a known dielectric constant. The pKa value of PCP adsorbed to membranes was always greater than the standard pKa value and it increased with the membrane's negative charge. The pKa value sequence in 0.1 M KCl was 6.68 (PG), 6.32 (PG/Chol = 70:30 mole fractions), 5.97 (PC), and 5.75 (PC/Chol = 70:30). The intrinsic pKa values of PCP in membranes were 5.2-5.4 (PG) and 5.5-6.0 (PC). Estimates of the dielectric constant of PCP's ionization site in membranes yielded 10-22 (PC) and 27-37 (PG). Cholesterol facilitated the release of the hydrogen ion from membrane-bound PCP. Measurements of pH dependence of PCP-induced membrane electrical conductivity. pH values of conductivity maxima were always greater than the standard pKa of PCP, and their sequence corresponded to that of the pKa values of membrane-bound PCP. The anomalous properties of PCP as a Class 2 uncoupler are due to PCP's lipophilic character. In response to a low dielectric constant of the adsorption/ionization site, the physicochemical characteristics of PCP adsorbed to membranes are different from the standard values--a fact that needs to be taken into account in the development of models of PCP's toxicity.