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At least 217 records · Page 12Linked to original sources
PubMed1984

Oxygen-18 incorporation into malic acid during nocturnal carbon dioxide fixation in crassulacean acid metabolism plants. A new approach to estimating in vivo carbonic anhydrase activity.

Crassulacean acid metabolism (CAM) plants fix carbon dioxide at night by the carboxylation of phosphoenolpyruvate. If CO2 fixation is conducted with 13C18O2 , then in the absence of carbonic anhydrase, the malate formed by dark CO2 fixation should also contain high levels of carbon-13 and oxygen-18. Conversely, if carbonic anhydrase is present and highly active, oxygen exchange between CO2 and cellular H2O will occur more rapidly than carboxylation, and the [13C] malate formed will contain little or no oxygen-18 above the natural abundance level. The presence of oxygen-18 in these molecules can be detected either by nuclear magnetic resonance (using the oxygen-18 effect on the carbon-13 chemical shift of the carboxyl carbon) or by mass spectrometry (comparing the ions at three and five units above the molecular weight with that one unit above). Studies of phosphoenolpyruvate carboxylase in the presence and absence of carbonic anhydrase in vitro confirm the validity of the method. When CAM plants are studied by this method, we find that most species show incorporation of a significant amount of oxygen-18. Comparison of these results with results of isotope fractionation and gas exchange studies permits calculation of the in vivo activity of carbonic anhydrase toward HCO-3 compared with that of phosphoenolpyruvate carboxylase. The ratio (carbonic anhydrase activity/phosphoenolpyruvate carboxylase activity) is species dependent and varies from a low of about 7 for Ananas comosus to values near 20 for Hoya carnosa and Bryophyllum pinnatum , 40 for Kalancho ë daigremontiana , and 100 or greater for Bryophyllum tubiflorum , Kalancho ë serrata, and Kalancho ë tomentosa. Carbonic anhydrase activity increases relative to phosphoenolpyruvate carboxylase activity at higher temperature.

Carbon Dioxide↗
PubMed1997

Potentially Macrocyclic Peptidyl Boronic Acids as Chymotrypsin Inhibitors.

The possibility of forming a peptide boronate adduct in a serine protease active site that mimics the first tetrahedral intermediate in the peptide hydrolysis mechanism was explored with the complex boronic acid analogs 7, 8-OH, and 8-NH(2)(). In these structures, the P(1) and P(2) residues and the P(1)'-P(3)' residues are connected through the P(2) and P(1)' side chains, to encourage formation of the diester or amide-ester adducts via macrocyclization. These inhibitors were assembled from suitably protected derivatives of 2,4-diaminobutanoic acid or 2,4-diaminopentanoic acid (11), borophenylalanine (12), aspartic acid, malic acid or the substituted malic acid analog 13, and Leu-Arg dipeptide. Stereoselective syntheses were developed for the (S,S)-2,4-diaminopentanoate 11 and for the (S,S)-beta-isobutylmalate 13 derivatives. The complex peptidyl boronates 7 (K(i) = 26 nM) and 8-OH (68 nM) are potent inhibitors of alpha-chymotrypsin; however, the affinity of 7 is neither time- nor pH-dependent, and it is only moderately greater than that found for comparison compounds like 8-H (114 nM), 9 (356 nM), and 10 (219 nM) that cannot cyclize or form a diester adduct.

Journal Article↗
PubMed2001

pH-dependent investigations of vanadium(V)-peroxo-malate complexes from aqueous solutions. In search of biologically relevant vanadium(V)-peroxo species.

The established biochemical potential of vanadium has spurred considerable research interest in our lab, with specific focus on pertinent synthetic studies of vanadium(III) with a biologically relevant, organic, dicarboxylic acid, malic acid, in aqueous solutions. Simple reactions between VCl3 and malic acid in water, at different pH values, in the presence of H2O2, led to the crystalline dimeric complexes (Cat)4[VO(O2)(C4H3O5)]2*nH2O (Cat = K+, n = 4, 1; Cat = NH4+, n = 3, 2) and K2[VO(O2)(C4H4O5)]2*2H2O (3). All three complexes were characterized by elemental analysis, FT-IR, and UV/visible spectroscopies. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a = 8.380(5) A, b = 9.252(5) A, c = 13.714(8) A, beta = 93.60(2) degrees, V = 1061(1) A3, and Z = 4. Compound 2 crystallizes in the triclinic space group P1, with a = 9.158(4) A, b = 9.669(4) A, c = 14.185(6) A, alpha = 104.81(1) degrees, beta = 90.31(1) degrees, gamma = 115.643(13) degrees, V = 1085.0(7) A(3), and Z = 2. Compound 3 crystallizes in the monoclinic space group P2(1)/c, with a = 9.123(8) A, b = 9.439(8) A, c = 10.640(9) A, beta = 104.58(3) degrees, V = 887(1) A3, and Z = 2. The X-ray structures showed that, in 1 and 2, the dimers consist of two (V(V)=O)2O2 rhombic units to which two malate ligands are attached. The ligands are triply deprotonated and, as such, they coordinate to vanadium(V), promoting a pentagonal bipyramidal geometry. In 3, the dimeric (V(V)=O)2O2 rhombic unit persists, with the two doubly deprotonated malate ligands coordinated to the vanadium(V) ions. UV/vis and EPR spectroscopic studies on the intermediate blue solutions of the synthesis reactions of 1-3 support the existence of vanadyl-containing dimeric species. These species further react with H2O2 to yield oxidation of V(IV)2O2 to V(V)2O2 and coordination of the peroxide to vanadium(V). From the collective data on 1-3, it appears that pH acts as a decisive factor in dictating the structural features of the isolated complexes. The details of the introduced structural differentiation in the reported complexes, and their potential relevance to vanadium(V) dicarboxylate systems in biological media are dwelled on.

Crystallography, X-Ray↗
PubMed2006

[Relationships between cadmium accumulation and organic acids in leaves of Solanum nigrum L. as a cadmium-hyperaccumulator].

The influence of different cadmium concentrations on the organic acid level in leaves of the Cd hyperaccumulator, Solanum nigrum L., in particular, the relationship of organic acids with Cd accumulation in S. nigrum was investigated based on the pot-culture experiment. The results showed that the Cd concentration in S. nigrum leaves exceeded 100 microg x g(-1), the threshold value used to define Cd-hyperaccumulators, and the bioaccumulation coefficient of cadmium in shoots of S. nigrum was higher than 1 when Cd concentration in soil was 25 microg x g(-1). The level of organic acids in leaves of S. nigrum had significant differences between the seedling stage and the mature stage. At the seedling stage, the sequence of organic acids in leaves of S. nigrum was acetic acid> tartaric acid> malic acid> citric acid. On the contrary, the accumulation of organic acids in S. nigrum at the mature stage was approximately in the following sequence malic acid> tartaric acid, acetic acid> citric acid. The significant positive correlation between Cd accumulation in leaves of S. nigrum and the concentration of tartaric acid in leaves of S. nigrum was observed at the seedling stage, whereas there was a significant positive correlation between Cd accumulation in leaves of S. nigrum and both acetic and citric acid concentrations at the mature stage. These results indicated that tartaric, acetic and citric acids in leaves of S. nigrum might act as the indication of Cd hyperaccumulation.

Acetic Acid↗
PubMed2003

The role of glycolysis and gluconeogenesis in the cytoprotection of neuroblastoma cells against 1-methyl 4-phenylpyridinium ion toxicity.

1-Methyl-4-phenylpyridinium (MPP+) is a mitochondrial Complex I inhibitor and is frequently used to investigate the pathological degeneration of neurons associated with Parkinson's disease (PD). In vitro, extracellular concentration of glucose is one of the most critical factors in establishing the vulnerability of neurons to MPP+ toxicity. While glucose is the primary energy fuel for the brain, central nervous system (CNS) neurons can also take up and utilize other metabolic intermediates for energy. In this study, we compared various monosaccharides, disaccharides, nutritive/non-nutritive sugar alcohols, glycolytic and gluconeogenic metabolic intermediates for their cytoprotection against MPP+ in murine brain neuroblastoma cells. Several monosaccharides were effective against MMP+ (500 microM) including glucose, fructose and mannose, which restored cell viability to 109 +/- 5%, 70 +/- 5%, 99 +/- 3% of live controls, respectively. Slight protective effects were observed in the presence of 3-phosphoglyceric acid and glucose-6-phosphate; however, no protective effects were exhibited by galactose, sucrose, sorbitol, mannitol, glycerol or various gluconeogenic and ketogenic amino acids. On the other hand, fructose 1,6 bisphosphate and gluconeogenic energy intermediates [pyruvic acid, malic acid and phospho(enol)pyruvate (PEP)] were neuroprotective against MPP+. The gluconeogenic intermediates elevated intracellular levels of ATP and reduced propidium iodide (PI) nucleic acid staining to live controls, but did not alter the MPP(+)-induced loss of mitochondrial O2 consumption. These data indicate that malic acid, pyruvic acid and PEP contribute to anaerobic substrate level phosphorylation. The use of hydrazine sulfate to impede gluconeogenesis through PEP carboxykinase (PEPCK) inhibition heightened the protective effects of energy substrates possibly due to attenuated ATP demands from pyruvate carboxylase (PC) activity and pyruvate mitochondrial transport. It was concluded from these studies that several metabolic intermediates are effective in fueling anaerobic glycolysis during mitochondrial inhibition by MPP+.

1-Methyl-4-phenylpyridinium↗
PubMed2002

[Comparison of effect on S.mutans producing acid ability between organic weak acid and fluoride].

OBJECTIVE: To figure out the effects of organic weak acids, benzoate, citric acid and malic acid on the main cariogenic bacteria S.mutans Ingbritt. To evaluate the possibility of above weak acids as anti-caries reagents. METHODS: S.mutans Ingbritt was inoculated into tryptic soy broth containing different concentrations of fluoride, benzoate, citric acid and malic acid, grew in anaerobic conditions at 37 degrees centigrade for 48h. The final pH values of suspension were measured. RESULTS: Fluoride had best inhibitory effect on S.mutans Ingbritt in low concentrations, whereas other 3 weak acids, benzoate, citric acid and malic acid could inhibit S.mutans Ingbritt in a higher concentrations. The order of effectiveness was fluoride>malic acid>benzoate>citric acid. CONCLUSION: Fluoride has the best inhibitory effect on S.mutans producing acid ability. Though weak acids benzoate, malic acid and citric acid in high concentration had different inhibitory effects on S.mutans Ingbritt, however high concentration of organic acids can make enamel demineralization.

English Abstract↗
PubMed2002

[Effect of low molecular weight organic acids on inorganic phosphorus transformation in red soil and its acidity].

Red soil samples collected from southern Hubei province and northern Jiangxi province were tested to analyze their inorganic phosphorus fractions, pH and active aluminum after incubated with added various organic acids. The results indicated that application of organic acids increased the content of Ca2-P in both red soils, in the order of citric acid > malic acid > succinic acid > acetic acid, did not affect the contents of Ca8-P and Ca10-P, but usually reduced Fe-P, Al-P and O-P. The pH values of the soils treated by organic acids, except for acetic acid, were reduced by 0.65-1.96, compared with the control. Soil active Al extracted with 0.02 mol.L-1 CaCl2 in treatments with citric, malic and succinic acid was 5.7-51.3 times as the control, and Al extracted with 1 mol.L-1 KCl also increased 4.0-67.3 times. However, acetic acid had little influence on active soil Al. It was concluded that in red soils, organic acid could improve phosphorus availability, but enhance the soil toxicity caused by active Al.

Acids↗
PubMed2006

[Effects of organic acids on Cd desorption of South China red soil].

Cadmium (Cd) pollution greatly threatens the environment of South China, where the economy developed very fast during last 20 years. In this paper, batch experiments were conducted to study the effects of three organic acids and their mixed solutions on the Cd desorption of red soil in this region. The results showed that oxalic acid and malic acid retarded the Cd desorption, but oxalic acid promoted it when the concentration was 20 mmol x L(-1) and soil pH value was higher than 5.0. With the increase of soil pH, Cd desorption decreased rapidly in the presence of oxalic acid and malic acid. Citric acid retarded Cd desorption at pH < 5.0, but promoted it at pH > 5.0. When the concentration of citric acid was 2 mmol x L(-1) and pH value changed from 3.0 to 7.0, Cd desorption declined first, increased then, and declined again. But, at the citric acid concentration of 20 mmol x L(-1), Cd desorption declined first till pH 4.0, and increased then till pH 7.0. At low pH (3.0 and 4.0), malic acid desorbed most Cd; while at high pH (5.0-7.0), citric acid desorbed most Cd. The Cd desorption rate was much higher in the presence of citric acid than oxalic acid and malic acid. Organic acids did not interactive effect on Cd desorption. The Cd desorption rate by mixed acids was within the range of that by single acid alone.

Adsorption↗