Effect Of MgCl Research Articles

Hydration mechanism of hydrated magnesium citrate: The effects of MgCl2

AbstractIn this study, the evolutions of kinetic parameters, such as hydration temperature, pH, and electrical conductivity, were observed to investigate the hydration mechanism of hydrated magnesium citrate (HMC). Additionally, the effects of MgCl2 on the hydration behavior of HMC and the working performance of its bonded castables were also investigated. The results show that the hydration mechanism of HMC is dissolution–precipitation, and its hydration product is magnesium citrate tetrahydrate [Mg(H2O)6] [MgC6H5O7(H2O)n]2∙(8‐2n)H2O. The hydration process of HMC is controlled by the concentration of the C6H6O72− ions. MgCl2 could inhibit the ionization of HMC, thereby delaying the hydration progress of HMC. The second exothermic peak was delayed from 1 to 4.8 h with increased MgCl2 content to 1.0 wt.%. The working performance of HMC‐bonded castables could be improved by adding MgCl2. After adding MgCl2, the setting time, flow value, and cold modulus of rupture of HMC‐bonded castables increased by 26.7%, 25.2%, and 8.8%, respectively, while the porosity decreased by 12%.

Pengekstrakan Amonia-Nitrogen dan Ortofosfat daripada Efluen Kilang Sawit dalam Bentuk Struvit

Ammonia-nitrogen (NH<sub>3</sub>-N) and orthophosphate (PO<sub>4</sub><sup>3-</sup>) contain in palm oil mill effluent will cause toxicity to aquatic life and polluted water source. However, these substances could be use as fertilizer for plant. Nitrogen and phosphorus are the mandatory nutrient source for the plant growth. This study studied the effect of pH and magnesium weight on the effectiveness of the extraction of ammonia-nitrogen (NH<sub>3</sub>-N) and orthophosphate (PO<sub>4</sub><sup>3-</sup>) from palm oil mill effluent (POME) in the form of struvite (MgNH<sub>4</sub>PO<sub>4</sub>•6H<sub>2</sub>O). The effect of pH on percent removal of NH<sub>3</sub>-N and PO<sub>4</sub><sup>3-</sup> from POME was studied by manipulating the pH of POME at constant the weight of magnesium chloride (MgCl<sub>2</sub>). Meanwhile, the effect of MgCl<sub>2</sub> on the percentage removal of NH<sub>3</sub>-N and PO<sub>4</sub><sup>3-</sup> from POME was studied by manipulating the weight of MgCl<sub>2</sub> at constant pH of POME. The concentrations of NH<sub>3</sub>-N and PO<sub>4</sub><sup>3-</sup> were determined using spectrophotometers and struvites were characterized using fourier-transform infrared (FTIR). This study showed that pH is an important factor in the extraction of NH<sub>3</sub>-N and PO<sub>4</sub><sup>3-</sup> ions in the form of struvit. pH 11.5 is the optimum pH to achieve the effective extraction process of NH<sub>3</sub>-N and PO<sub>4</sub><sup>3-</sup> from POME in the form of struvit. Addition of the MgCl<sub>2</sub> did not have a significant effect on the extraction process because POME contained sufficient magnesium ions for the extraction process. The highest NH<sub>3</sub>-N and PO<sub>4</sub><sup>3−</sup> removal was attained at pH 11.5 with the addition of 0.5 g MgCl<sub>2</sub>. 93.72% NH<sub>3</sub>-N and 86.15% PO<sub>4</sub><sup>3-</sup> were removed from POME in struvit extraction process. The resulting struvit yield was also identified through FTIR analysis by the existence of O-H bond, N-H bond, and P-O bond.

Effects of MgCl2 Solution Pretreatment at Room Temperature on the Pyrolytic Behavior of Pubescens and the Properties of Bio-oil Obtained

Pyrolytic behavior of pubescens samples pretreated by 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.% MgCl2 solution, and HCl solution (with same pH value as 5 wt.% MgCl2 solution, namely pH=5.11) at roo...

Effect of MgCl2 on Energy Generation by Reverse Electrodialysis

Effect of MgCl₂ on Energy Generation by Reverse Electrodialysis

Effect of MgCl 2 additives on the H-desorption properties of Li–N–H system

Li–N–H system, as a representative of metal-N–H system, is regarded as one of the most promising hydrogen storage materials. Motivated by the ammonia mediated mechanism of Li–N–H system, the effect of MgCl 2 (which is an effective NH 3 sorbent) on this system is systematically investigated in this work. Three different mechanisms are proposed to explain the effects of MgCl 2 with different amount in the improvement of Li–N–H system. With small amount (<4 mol%), MgCl 2 can improve the H-desorption properties of Li–N–H system as an NH 3 sorbent. When the amount of MgCl 2 increases, the H-desorption properties of Li–N–H system can be improved further though Mg 2+ solid solution into LiNH 2. With the amount of MgCl 2 more than 25 mol%, the Li–N–H system changes into Li–Mg–N–H system by the reaction between MgCl 2 and LiNH 2. The Li–Mg–N–H system formed by this reaction exhibits a much better property than those of Li–Mg–N–H system reported before. It may provide a new idea to improve the metal-N–H system to meet the requirement of practical application.

Effect of MgCl&lt;sub&gt;2&lt;/sub&gt; on Germination, Growth and Biomass Allocation of the Radish CV. "Cherry Belle"

Problem statement: To determine the effect of MgCl2 on radish (Raphanus sativus), plants were grown in controlled environmental growth chambers and given one of three watering treatments; 0.01, 0.1 and 0 M (control) MgCl2. Approach: At high concentrations (0.1 M), MgCl2 was toxic resulting in very low (44%) germination rates and the subsequent death of all but three undersized plants over the 28 day growth period. Results: At lower concentrations (0.01 M), MgCl2 resulted in enhanced germination rates (5.55%) and a mass increase (39.54%) over the control. Conclusion/Recommendations: While low concentrations of MgCl2 resulted in an increase in total biomass, biomass allocation was shifted largely from roots to shoots (55.88% higher root/shoot ratio in the control).

Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single‐Centre and Ziegler–Natta Catalysts for Ethylene Polymerization

AbstractThe ability of a MgCl2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu2 with HCl gave high activity with TiCl4 but low activity with (n‐PrCp)2ZrCl2. High polymerization activities with the zirconocene were only obtained with supports of type MgCl2/AlRn(OEt)3−n prepared from the reaction of AlR3 with MgCl2 · 1.1EtOH. These supports are characterized by additional peaks in the X‐ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species.magnified image

Physical and functional interaction of human nuclear uracil-DNA glycosylase with proliferating cell nuclear antigen

Uracil residues arise in DNA by the misincorporation of dUMP in place of dTMP during DNA replication or by the deamination of cytosine in DNA. Uracil-DNA glycosylase initiates DNA base excision repair of uracil residues by catalyzing the hydrolysis of the N-glycosylic bond linking the uracil base to deoxyribose. In human cells, the nuclear form of uracil-DNA glycosylase (UNG2) contains a conserved PCNA-binding motif located at the N-terminus that has been implicated experimentally in binding PCNA. Here we use purified preparations of UNG2 and PCNA to demonstrate that UNG2 physically associates with PCNA. UNG2 co-eluted with PCNA during size exclusion chromatography and bound to a PCNA affinity column. Association of UNG2 with PCNA was abolished by the addition of 100 mM NaCl, and significantly decreased in the presence of 10 mM MgCl 2. The functional significance of the UNG2·PCNA association was demonstrated by UNG2 activity assays. Addition of PCNA (30–810 pmol) to standard uracil-DNA glycosylase reactions containing linear [ uracil- 3H]DNA stimulated UNG2 catalytic activity up to 2.6-fold. UNG2 activity was also stimulated by 7.5 mM MgCl 2. The stimulatory effect of PCNA was increased by the addition of MgCl 2; however, the dependence on PCNA concentration was the same, indicating that the effects of MgCl 2 and PCNA on UNG2 activity occurred by independent mechanisms. Loading of PCNA onto the DNA substrate was required for stimulation, as the activity of UNG2 on circular DNA substrates was not affected by the addition of PCNA. Addition of replication factor C and ATP to reactions containing 90 pmol of PCNA resulted in two-fold stimulation of UNG2 activity on circular DNA.

P.4.020 Effect of MgCl 2·6H 2O with vitamin B 6 on the emotional status and magnesium content in brain structures of rats fed with magnesium-deficient diet

P.4.020 Effect of MgCl 2·6H 2O with vitamin B 6 on the emotional status and magnesium content in brain structures of rats fed with magnesium-deficient diet

The Solubility of MgO in Molten MgCl&lt;SUB&gt;2&lt;/SUB&gt;-CaCl&lt;SUB&gt;2&lt;/SUB&gt; Salt

The solubility of MgO in molten MgCl 2 and CaCl 2 has been studied. In pure MgCl 2 , the MgO solubility was determined to be 0.63-2.90 mol5 at 1073-1373 K, while 0.24-0.63 mol% in pure CaCl 2 at 1223-1523 K. The effects ofMgCl 2 and CaO addition to CaCl 2 were investigated, and the solubility product of MgO was found to increase with the amount of MgCl 2 addition, while CaO addition did not affect significantly. They were explained in terms of the activity coefficient of oxide ion (O 2 - ) as well as the enthalpy of mixing for the MgO-CaCl 2 system. From the experimental results, the corrosion possibility of MgO refractory by Cl-containing gas was considered.

Detection of Escherichia coli O157:H7 using immunomagnetic separation and absorbance measurement

An assay system for detection of Escherichia coli O157:H7 was developed based on immunomagnetic separation of the target pathogen from samples and absorbance measurement of p-nitrophenol at 400 nm from p-nitrophenyl phosphate hydrolysis by alkaline phosphatase (EC 3.1.3.1) on the “sandwich” structure complexes (antibodies coated onto micromagnetic beads— E. coli O157:H7-antibodies conjugated with the enzyme) formed on the microbead surface. The effects of immunoreaction time, phosphate buffer concentration, pH and temperature on the immunomagnetic separation of E. coli O157:H7 from samples were determined and the conditions used for the separation were 1-h reaction time, 1.0×10 −2 M PBS, pH 8.0 and 33 °C in this system. The effects of MgCl 2 concentration, Tris buffer concentration, pH and temperature on the activity of alkaline phosphatase conjugated on the immuno-“sandwich” structure complexes were investigated after immunomagnetic separation of the target pathogen and the conditions used for the enzymatic amplification were 1.0×10 −4 M MgCl 2, 1.0 M Tris buffer, pH 8.0, 28 °C and 30-min reaction time during the assay. The selectivity of the system was examined and no interference from the other pathogens including Salmonella typhimurium, Campylobacter jejuni and Listeria monocytogenes was observed. Its working range was from 3.2×10 2 to 3.2×10 4 CFU/ml, and the relative standard deviation was 2.5–9.9%. The total detection time was less than 2 h.

Fetal exposure to magnesium chloride-adenosine triphosphate (MgCl2-ATP) results in alterations in cerebral blood flow and a metabolic acidosis

OBJECTIVE: Magnesium chloride-adenosine triphosphate (MgCl(2)-ATP), advocated as an adjunct treatment in shock resuscitation, might be useful for pregnant women who develop hypovolemia secondary to conditions such as placental abruption. The effects of this treatment on the fetus, however, have never been investigated. This study determined the direct, acute effects of MgCl(2)-ATP on fetal organ blood flow, hemodynamic measurements, and metabolic parameters before and after maternal hemorrhage. DESIGN: Experimental, randomized, nonblinded, control study. SETTING: Animal laboratory at a university research facility. SUBJECTS: This study was performed on 11 chronically instrumented, 123-day gestational age, pregnant ewes (term = 147 days) and their fetuses. INTERVENTIONS: Ewes were randomly allocated to either experimental (Expt, n = 5) or control (Cntl, n = 6) groups. After a 60-min baseline period, Expt fetuses received a 60-min iv infusion of MgCl(2)-ATP (150 &mgr;mole/hr each of MgCl(2) and ATP; at 3 mL/hr), and Cntl fetuses received an equivalent volume of 0.9% NaCl. After this infusion-only period, the infusion was continued, and ewes were intermittently bled over 1 hr for a total blood loss of 20 mL/kg (hemorrhage-plus-infusion period). After this, the infusions were continued, and ewes and fetuses were monitored for 1 additional hr (posthemorrhage period). Measurements: At the end of all periods, fetal and maternal blood pressures, blood gases, oxygen saturation, hemoglobin, serum electrolytes, and serum glucose concentrations were measured. At the end of the baseline, infusion-only, and hemorrhage-plus-infusion periods, fetal organ blood flows were determined using a fluorescent microsphere technique. Nonparametric statistics were used for comparisons (2-tailed, p </=.05). MAIN RESULTS: Maternal hemorrhage caused maternal hypotension, resulting in a decrease in fetal oxygen content and an increase in fetal hemoglobin and glucose concentrations. The changes were similar in both groups. In both groups, a progressive fetal metabolic acidosis developed during the hemorrhage period and it continued through the posthemorrhage period. This metabolic acidosis was more severe in the Expt fetuses and appeared to have started during the infusion-only period. There were no fetal deaths in either group. In the Cntl fetuses, there were increases from baseline after the hemorrhage-plus-infusion period in fetal adrenal (71%), brain (89%), and thymus (18%) blood flow and a decrease in muscle (-28%) blood flow. In the Expt fetuses, there were increases during the infusion-only period in adrenal (332%), myocardial (142%), and pancreatic (219%) blood flow and decreases in kidney (-25%) and skin (-75%) blood flow. These changes persisted during the hemorrhage-plus-infusion period. Most strikingly, regional cerebral blood flow in the Expt fetuses did not increase from baseline in any of the 10 brain areas sampled during the infusion-only period or following maternal hemorrhage. In Cntl fetuses, however, there was increase in blood flow in all 10 brain areas sampled following maternal hemorrhage. CONCLUSIONS: In healthy fetuses, direct MgCl(2)-ATP exposure caused metabolic acidosis and a redistribution of cardiac output to different organs. When the MgCl(2)-ATP fetuses were then subject to the effects of maternal hemorrhage, the expected increase in cerebral blood flow was not observed. Although an earlier study suggests that ATP may be beneficial to stressed fetuses when administered to mothers in labor, the direct effect of MgCl(2)-ATP appears to be potentially harmful by producing an acidosis and altering the normal fetal cerebral blood flow response to maternal hemorrhage.

Effect of MgCl2 and Phosphatidylglycerol on CaCl2-Mediated Recovery of Oxygen Evolution in a Photosystem II Complex Depleted of the 17 and 24 kDa Extrinsic Proteins

Abstract Phosphatidylglycerol (PG) is an anionic lipid of the thylakoid membrane of higher plant chloroplasts. PG was shown previously to stimulate the evolution of oxygen in intact pho­tosystem II (PSII) membranes [Fragata, M., Strzałka, K. and Nénonéné, E. K. (1991) J. Photochem. Photobiol. B: Biol 11, 329-342], In this work, a study was undertaken of the effect of MgCl2 and PG on the CaCl2-mediated recovery of oxygen evolution in a PSII complex depleted of the extrinsic proteins (EP) of molecular masses 17 kDa (EP17) and 24 kDa (EP24), hereunder designated d17.24PSII. This molecular system is structurally close to the PSII core complex of cyanobacteria and is therefore useful in the comparative analysis of PSII-PG relationships in cyanobacteria and the higher plants. This work reveals a new aspect of the thylakoid lipids role in the PSII function, namely the PG effect on intact PSII is observed as well in d17.24PSII. The results show that phosphatidylglycerol has the ability to compensate for the loss of EP17 and EP24 in the PSII complex. That is, PG restores the oxygen evolution in d17.24PSII incubated in the presence of MgCl2 and/or CaCl2 to the levels observed in native PSII. Moreover, the site of H2O degradation in d17.24PSII, including most probably the pool of calcium and chloride ions, would seem to be protected by phosphatidyl­glycerol. This suggests that one of the docking sites of PG in the PSII complex is near EP24, inasmuch as this extrinsic protein participates in the regulation of the affinity of the calcium and chloride ions to the water oxidation site. Furthermore, taking into account that in d17.24PSII the PSII core complex is directly exposed to PG, then the phospholipid effect reported here indicates that phosphatidylglycerol might be a functional effector and mem­brane anchor of the D1 protein in the PSII core complex as was shown recently in the cyanobacterium Oscillatoria chalybea [Kruse, O. and Schmid, G. H. (1995) Z. Naturforsch. 50c, 380-390],

Sensitivity of acetylcholinesterase molecular forms to inhibition by high MgCl 2 concentration

Previous studies have shown that the asymmetric (A 12) and the dimeric (G 2), but not the tetrameric (G 4), acetylcholinesterase (AChE) forms are inactivated by high MgCl 2: concentration (Perelman and Inestrosa (1989) Anal. Biochem. 180, 227–230). Here we show that the effect of MgCl 2 on AChE activity corresponds to an irreversible inhibition and is not due to environmental effects related to the different extraction media. The anchor domain in each AChE form was not involved in the differential MgCl 2 sensitivity. Monomers derived from the various AChE forms behave in a way similar to that of the original assembled forms. Purified AChE molecular forms showed the same sensitivity to MgCl 2, than the same enzyme forms studied in tissue extracts. Neither the affinity for the substrate nor the inhibition by excess substrate of the residual AChE activity were affected by high MgCl 2. concentration. Results indicate that the differences between the tetrameric enzyme and the other two AChE molecular forms occur at the level of the catalytic subunit, probably due to differential post-translational processing.

Effects of MgCl 2 on the release and recycling of heparan sulfate proteoglycans in a rat parathyroid cell line

Divalent cations, such as Mg 2+, Ba 2+, and Co 2+, are known to mimic the effects of Ca 2+ in parathyroid cells, but it is not clear whether the mechanism of their action is the same as that of Ca 2+. We have shown that extracellular Ca 2+ concentration ([Ca 2+] e) regulates the distribution and recycling of cell-surface heparan sulfate (HS) proteoglycans in a rat parathyroid cell line; at normal to high [Ca 2+] e (e.g., 2 m m) HS proteoglycans are primarily localized intracellularly, while at low [Ca 2+] e (0.05 m m) they are translocated to the cell surface and rapidly recycle (Takeuchi, Y., Sakaguchi, K., Yanagishita, M., Aurbach, G. D., and Hascall, V. C., 1990, J. Biol. Chem. 265, 13661–13668). We now show that a high concentration of Mg 2+ (8 m m) reduces the amount of recycling HS proteoglycans in low [Ca 2+] e. However, the primary effects of high Ca 2+ and high Mg 2+ on the recycling HS proteoglycans are different. High [Ca 2+] e causes translocation of HS proteoglycans to intracellular compartments, while high Mg 2+ stimulates cleavage of their core proteins and subsequent shedding of HS proteoglycans into the medium, thereby depleting the recycling molecules. However, high Mg 2+ does not induce shedding of HS proteoglycans in high [Ca 2+] e. The effects of Ba 2+ and Co 2+ were similar to those of Mg 2+, but Sr 2+ showed no significant effects on HS proteoglycan translocation. Otherwise, 8 m m Mg 2+ did not alter biosynthesis or intracellular catabolism of HS proteoglycans. These observations suggest that the recycling of HS proteoglycans in parathyroid cells is sensitive only to [Ca 2+] e, whereas several other divalent cations can deplete the recycling HS proteoglycans by a distinctly different mechanism. Thus, the mechanism by which Ca 2+ regulates the amounts of the recycling HS proteoglycans may be more physiological and play a functional role in parathyroid Cells.

Effects of MgCl 2 and ZnCl 2 additives on the porosity of formed coke

In this study, the effect of MgCl 2 and ZnCl 2 additives on the porosity of formed cokes produced from Soma-Turkey hard lignite was investigated. Previously, it was found that formed cokes manufactured from Soma non-caking hard lignite using sulphite liquor binder had an acceptable compressive strength (13.5 MPa) but lower porosity (38 vol%) than that of conventional cokes (41–55 vol%). To increase porosity, ZnCl 2 or MgCl 2 in varied amounts were added to the lignite sample. Addition of MgCl 2 and ZnCl 2 resulted, respectively, in 81.6 and 10.5% increases in the volume porosity of the formed cokes. Taking into consideration the porosity and compressive strength values demanded of metallurgical coke, the appropriate amounts of ZnCl 2 and MgCl 2 to be added were determined to be 6 and 1 wt%, respectively.

Salt-mediated interconversions and purification of malate synthase from germinating soybean cotyledons ( Glycine max. L.)

The effects of MgCl 2 and KCl on the structural properties of malate synthase from germinating soybean ( Glycine max. L.), were investigated. The enzyme was obtained from isolated glyoxysomes or from crude homogenates. It was clearly shown to undergo reversible structural interconversions depending on ionic strength as adjusted by MgCl 2 and KCl (membrane bound enzyme form, precipitable aggregates, soluble dimeric and decameric forms). These interconversions were taken advantage of in the purification procedure.

Destabilization of the duplex and the high-salt Z-form of poly(dG-methyl 5dC) by substitution of ethyl for the 5-methyl group

The B-to-Z conformational transition of poly(dG-dC) is highly promoted by 5-methyl substitution of the dC moiety, i.e. in poly(dG-methyl 5dC). By the synthesis of a new poly(dG-dC) analogue, poly(dG-ethyl 5dC), the effect of a longer alkyl-chain substituent of dC on structure and conformation has been studied with ultraviolet absorption melting profiles and circular dichroism spectroscopy. The 5-ethyl substituent in poly(dG-ethyl 5dC) destabilizes the duplex structure against thermal denaturation compared with both poly(dG-methyl 5dC) and poly(dG-dC). C.d. studies also reveal that for the high-salt B-Z transition of poly(dG-ethyl 5dC) a higher NaCl concentration is required than for that of poly(dG-methyl 5dC), although much lower than for poly(dG-dC). However low-salt Z-DNA in poly(dG-ethyl 5dC) shows unique features, e.g. it needs no divalent cations to be stable. The low-salt B-Z transition of poly(dG-ethyl 5dC) can also be observed by the absorption-temperature melting profile, in constrast to both poly(dG-methyl 5dC) and poly(dG-dC). The effects of MgCl 2 concentration, temperature, acid pH and trifluorethanol on the conformation of poly(dG-ethyl 5dC) have also been determined.

Induction of bitter pit in apple

A field study was conducted to induce bitter pit in cultivar ‘Sundale Spur Golden Delicious’ ( Malus domestica Borkh.) apple. Fruiting spurs were sprayed with 1% (w/v) CaCl 2 and 1% (w/v) MgCl 2 every 10 days, beginning 5 days after full bloom, and/or shaded with brown paper bags. The effect of MgCl 2 spray and bag + MgCl 2 treatments on the fruiting spurs was increased bitter pit incidence, decreased fruit calcium, increased fruit magnesium and potassium, and decreased number of fruit per spur. Bagging the fruit resulted in a 4-fold increase in bitter pit incidence, and a significant reduction in fruit calcium content and fruit weight over the control. In contrast, CaCl 2 spray slightly reduced bitter pit, increased fruit calcium, reduced fruit magnesium and increased the number of fruit per spur. The incidence of bitter pit ranged from 8% (CaCl 2 spray alone) to 88% (bag + MgCl 2). Overall, the combinations of bagging and cation sprays induced a wide range of bitter pit incidence in apple fruit which can be reliably used for future study of the disorder.

Free Fatty Acids Regulate Two Galactosyltransferases in Chloroplast Envelope Membranes Isolated from Spinach Leaves

Effects of MgCl(2) and free fatty acids (FFA) on galactolipid:galactolipid galactosyltransferase (GGGT) and UDP-galactose: 1,2-diacylglycerol galactosyltransferase (UDGT) in chloroplast envelope membranes isolated from spinach (Spinacia oleracea L.) leaves were examined. GGGT activity was sigmoidally stimulated by MgCl(2) with a saturated concentration of more than 5 millimolar. Free alpha-linolenic acid (18:3) caused a drastic increase in GGGT activity under limiting concentrations of MgCl(2), without affecting its maximum activity at higher MgCl(2) concentrations. Free 18:3 alone did not affect the GGGT activity. The effective species of FFA for the stimulation of GGGT activity in the presence of MgCl(2) were unsaturated 16- and 18-carbon fatty acids. GGGT activity was also stimulated by 18:3 in the presence of MnCl(2), CaCl(2) and a high concentration of KCl in place of MgCl(2). UDGT activity was hyperbolically enhanced by MgCl(2) with a saturated concentration of 1 to 2 millimolar. In contrast to GGGT, UDGT was severely inhibited by 18:3, and MgCl(2)-induced stimulation was completely abolished by 18:3. Unsaturated 16- and 18-carbon fatty acids were more inhibitory to UDGT than the saturated acids. The dependence of GGGT activity on monogalactosyldiacylglycerol (MGDG) and MgCl(2) concentrations was identical in the envelope membranes isolated from non- and ozone (0.5 microliter/liter)-fumigated spinach leaves, indicating that GGGT remained active in the leaves during ozone fumigation. The results are discussed in relation to the regulation of galactolipid biosynthesis by the endogenous FFA in the envelopes and to the involvement of GGGT in the triacylglycerol synthesis from MGDG in ozone-fumigated leaves.