The Regulation of Acetyl Coenzyme A Synthesis in Chloroplasts

1985 ◽  
Vol 40 (7-8) ◽  
pp. 496-502 ◽  
Author(s):  
Hans-Jürgen Treede ◽  
Klaus-Peter Heise
Keyword(s):  
Pyruvate Dehydrogenase Complex ◽  
Acetyl Coa ◽  
Ph Optimum ◽  
Spinach Chloroplasts ◽  
Branched Chain Amino Acid ◽  
Pea Seedlings ◽  
Low Concentrations ◽  
Acetyl Coa Synthesis ◽  
High Concentrations ◽  
Branched Chain

Abstract The enzymatic activities of the pyruvate dehydrogenase complex (PDC) and acetyl-CoA synthetase (ACS) have been compared in extracts of plastids isolated from spinach leaves and from both green and etiolated pea seedlings. A ll plastid preparations were shown to be capable of synthesizing acetyl-CoA, not only via acetyl-CoA synthetase, but also via the pyruvate dehydroge­ nase complex, though, with different activities. Both pathways are apparently under metabolic control. Thus, the substrate levels in photosynthetically active spinach chloroplasts appear to favor acetyl-CoA synthesis via ACS (apparent Km for acetate of 0.1 mм) , because calculated stromal pyruvate levels (0.1 m M) appear to limit its formation via the PDC (apparent Km for pyruvate of 0.2-0.3 nм) . In spinach chloroplasts, therefore, the PDC pathway seems to be predominantly involved in providing precursors for branched-chain amino acid biosynthesis (vali­ne, leucine and isoleucine). Acetyl-CoA, synthesized via ACS, may additionally function as an inhibitor of the chloroplast PD C , because, as in mitochondria, relatively low concentrations of the end products NADH and acetyl-CoA strongly inhibit the PD C in chloroplast extracts. On the other hand, comparatively high concentrations of MgATP, a cofactor for ACS, inhibited the PDC complex. The pH optimum of about 8 and the high Mg-requirement distinguishes both enzymes from mitochondrial PDC and reflects an accomodation to stromal conditions in photosynthetically active chloroplasts.

scholarly journals Kinetic properties of the partially purified pyruvate dehydrogenase complex of ox brain

1973 ◽  
Vol 131 (1) ◽  
pp. 31-37 ◽  
Author(s):  
John P. Blass ◽  
Carole A. Lewis
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Tricarboxylic Acid Cycle ◽  
Pyruvate Dehydrogenase Complex ◽  
Kinetic Properties ◽  
Acetyl Coa ◽  
Ph Optimum ◽  
Michaelis Constants ◽  
High Concentrations ◽  
Similar Preparation ◽  
Dehydrogenase Complex

The properties of a purified preparation of the pyruvate dehydrogenase complex from ox brain have been compared with those of a similar preparation from ox kidney. A broad pH optimum around 7.8, similar dependence on ionic strength, and independence of the nature of the buffer anions or cations characterized preparations from both tissues. Michaelis constants for the binding of pyruvate, thiamin pyrophosphate, NAD+ and CoA were also similar. Enzyme from both tissues was inhibited by NADH, by copper and other heavy metals, by high concentrations of tricarboxylic acid-cycle intermediates, and by preincubation with ATP. Acetyl-CoA itself did not appear to inhibit these preparations, although some commercial preparations of acetyl-CoA did contain an inhibitor. Although oxaloacetate and α-oxobutyrate were weak inhibitors, a number of other α-oxo acids including phenylpyruvate did not inhibit. The properties of the pyruvate dehydrogenase complex from brain and kidney appeared similar.

scholarly journals Temperature and the regulation of enzyme activity in poikilotherms. Properties of rainbow-trout fructose diphosphatase

1969 ◽  
Vol 111 (3) ◽  
pp. 287-295 ◽  
Author(s):  
H. W. Behrisch ◽  
P. W. Hochachka
Keyword(s):  
Enzyme Activity ◽  
Rainbow Trout ◽  
Temperature Adaptation ◽  
Temperature Dependent ◽  
Ph Optimum ◽  
Physiological Temperature ◽  
Low Concentrations ◽  
High Concentrations ◽  
Regulation Of Enzyme Activity ◽  
Hill Plots

1. The properties of fructose diphosphatase from the liver of rainbow trout (Salmo gairdnerii) were examined over the physiological temperature range of the organism. 2. Saturation curves for substrate (fructose 1,6-diphosphate) and a cofactor (Mg2+) are sigmoidal, and Hill plots of the results suggest a minimum of two interacting fructose 1,6-diphosphate sites and two interacting Mg2+ sites per molecule of enzyme. 3. Mn2+-saturation curves are hyperbolic, and the Ka for Mn2+, which inhibits the enzyme at high concentrations, is 50–100-fold lower than the Ka for Mg2+. 4. Fructose diphosphatase is inhibited by low concentrations of AMP; this inhibition appears to be decreased and reversed by increasing the concentrations of Mg2+ and Mn2+. Higher concentrations of AMP are required to inhibit the trout fructose diphosphatase in the presence of Mn2+. 5. The affinities of fructose diphosphatase for fructose diphosphate and Mn2+ appear to be temperature-independent, whereas the affinities for Mg2+ and AMP are highly temperature-dependent. 6. The pH optimum of the enzyme depends on the concentrations of Mg2+ and Mn2+. In addition, pH determines the Ka for Mg2+; at high pH, Ka for Mg2+ is lowered. 7. The enzyme is inhibited by Ca2+ and Zn2+, and the inhibition is competitive with respect to both cations. 8. The possible roles of these ions and AMP in the modulation of fructose diphosphatase and gluconeogenic activity are discussed in relation to temperature adaptation.

scholarly journals Comparative Analyses of Volatile Metabolites Associated With Gene Expression From Non-climacteric and Climacteric Melon.

2021 ◽  
Author(s):  
Kamila Karoline de Souza Los ◽  
Michelle Orane Schemberger ◽  
Leticia Reis ◽  
Marília Aparecida Stroka ◽  
Caroline Weigert Galvão ◽  
...  
Keyword(s):  
Amino Acid ◽  
Economic Importance ◽  
Important Species ◽  
Phenotypic Differences ◽  
Branched Chain Amino Acid ◽  
Volatile Products ◽  
High Concentrations ◽  
Acid Pathway ◽  
Branched Chain ◽  
Cucumis Melo L

Abstract Melon (Cucumis melo L.) is an important species in the cucurbits family with a large economic importance in the world. Two melon cultivars commercially important in Brazil are the cultivars ‘Yellow’ and ‘Gaúcho’. In addition to the economic importance, these two cultivars display phenotypic differences in aroma, a major trait determining fruit quality. Volatile organic compounds (VOC) impart the different aroma found in these fruit and its biosynthesis is associated with fatty acid and amino acid metabolism. Using SPME-GC–MS and RT-qPCR techniques, volatile production and expression of seven genes (CmLOX9, CmLOX18, CmBCAT1, CmArAT1, CmPDC1, CmADH1 and CmAAT1) were determined during maturation and ripening. The climacteric melon ‘Gaúcho’ had a greater number and higher concentration of volatiles than that in the non-climacteric ‘Yellow’ melon. 2-Methylallyl acetate, 4-amino-1-butanol, 2-methylbutanol and ethyl 2-methylpropanoate were found in high concentrations in ripe climacteric ‘Gaúcho’ melons and were major contributors to its strong fruity aroma, but high concentrations of these volatiles were not found in non-climacteric ‘Yellow’ melons. The lipid pathway played a strong role in determining aroma composition in non-climacteric ‘Yellow’ melons. Most volatiles decreased during maturation and ripening explaining the non-aromatic characteristic of this cultivar. In climacteric ‘Gaúcho’ melons, the amino acid pathway was the main one related to the biosynthesis of esters, which contribute to the aroma of this cultivar. Volatile products of the branched chain amino acid pathway correlated with CmADH1 and CmAAT1 expression demonstrating their role in volatile synthesis of this climacteric melon cultivar. In addition, CmPDC1 contributes to the formation of aldehydes at the beginning of this pathway.

scholarly journals Acylcarnitine Profiles in Plasma and Tissues of Hyperglycemic NZO Mice Correlate with Metabolite Changes of Human Diabetes

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Anna Weiser ◽  
Pieter Giesbertz ◽  
Hannelore Daniel ◽  
Britta Spanier
Keyword(s):  
Amino Acid ◽  
Principal Component ◽  
The Metabolic Syndrome ◽  
Branched Chain Amino Acid ◽  
Nzo Mice ◽  
Obesity And Diabetes ◽  
Human Diabetes ◽  
High Concentrations ◽  
Branched Chain

The New Zealand obese (NZO) mouse is a polygenic model for obesity and diabetes with obese females and obese, diabetes-prone males, used to study traits of the metabolic syndrome like type 2 diabetes mellitus (T2DM), obesity, and dyslipidaemia. By using LC-MS/MS, we here examine the suitability of this model to mirror tissue-specific changes in acylcarnitine (AC) and amino acid (AA) species preceding T2DM which may reflect patterns investigated in human metabolism. We observed high concentrations of fatty acid-derived ACs in 11 female mice, high abundance of branched-chain amino acid- (BCAA-) derived ACs in 6 male mice, and slight increases in BCAA-derived ACs in the remaining 6 males. Principal component analysis (PCA) including all ACs and AAs confirmed our hypothesis especially in plasma samples by clustering females, males with high BCAA-derived ACs, and males with slight increases in BCAA-derived ACs. Concentrations of insulin, blood glucose, NEFAs, and triacylglycerols (TAGs) further supported the hypothesis of high BCAA-derived ACs being able to mirror the onset of diabetic traits in male individuals. In conclusion, alterations in AC and AA profiles overlap with observations from human studies indicating the suitability of NZO mice to study metabolic changes preceding human T2DM.

scholarly journals Melatonin Reprograms Glucose Metabolism in Cancer Cell Mitochondria

2019 ◽  
Vol 1 (3) ◽  
pp. 52-61
Author(s):  
Russel J. Reiter ◽  
Keyword(s):  
Cancer Cells ◽  
Cancer Cell ◽  
Pyruvate Dehydrogenase Complex ◽  
Cancer Growth ◽  
Cell Phenotype ◽  
Acetyl Coa ◽  
History Of ◽  
Cancer Phenotype ◽  
High Concentrations ◽  
The Warburg Effect

Melatonin has a long history of studies which confirm its ability to inhibit cancer growth. Melatonin is present in high concentrations in the mitochondria of normal cells but is likely absent from the mitochondria of cancer cells, at least when isolated from tumors harvested during the day. Herein, we hypothesize that melatonin’s absence from cancer cell mitochondria prevents these organelles from metabolizing pyruvate to acetyl coenzyme A (acetyl-CoA) due to suppression of the activity of the enzyme pyruvate dehydrogenase complex (PDC), the enzyme that catalyzes the conversion of pyruvate to acetyl-CoA. This causes cancer cells to metabolize glucose to lactate in the cytosol (the Warburg effect). Since cancer cell mitochondria can take up nighttime pineal-derived melatonin from the blood, the indoleamine predictably promotes the conversion of pyruvate to acetyl-CoA in the mitochondria during the night. Thus, while cancer cells exhibit a typical cancer phenotype during the day, at night cancer cells have a more normal cell phenotype. Via similar actions, melatonin probably overcomes the insensitivity of cancers to chemotherapies. Hopefully, the hypothetical processes proposed herein will soon be experimentally tested.

scholarly journals Intermediates of peroxisomal β-oxidation. A study of the fatty acyl-CoA esters which accumulate during peroxisomal β-oxidation of [U-14C]hexadecanoate

1990 ◽  
Vol 270 (1) ◽  
pp. 175-180 ◽  
Author(s):  
K Bartlett ◽  
R Hovik ◽  
S Eaton ◽  
N J Watmough ◽  
H Osmundsen
Keyword(s):  
Lactate Dehydrogenase ◽  
Chain Length ◽  
Full Range ◽  
Fatty Acyl ◽  
Acetyl Coa ◽  
Low Concentrations ◽  
High Concentrations ◽  
Rate Limiting

1. 14C-labelled fatty acyl-CoA esters resulting from β-oxidation of [U-14C]hexadecanoate by peroxisomal fractions isolated from rats treated with clofibrate showed the presence of the full range of saturated intermediates down to acetyl-CoA. 2. The pattern of intermediates generated was fairly constant. At low concentrations of [U-14C]hexadecanoate (50 microM), decanoyl-CoA was present in lowest amounts. At higher concentrations of [U-14C]hexadecanoate (greater than 100 microM), all intermediates of chain length shorter than 12 carbon atoms (except acetyl-CoA) were present at similar low concentrations; the process of β-oxidation now resembling chain-shortening of hexadecanoate by two cycles of β-oxidation. 3. In the absence of an NAD(+)-regenerating system [pyruvate and lactate dehydrogenase (EC 1.1.1.28)] 2-enoyl- and 3-hydroxyacyl-CoA esters were generated, suggesting that re-oxidation of NADH is essential for optimal rates of peroxisomal β-oxidation in vitro. 4. At high concentrations of [U-14C]hexadecanoate (greater than 100 microM), 3-oxohexadecanoyl-CoA was produced, suggesting that thiolase (acetyl-CoA acetyltransferase; EC 2.3.1.9) can become rate-limiting for peroxisomal β-oxidation.

Requirements for branched chain amino acids and their interactions in the nematode Caenorhabditis elegans

Nematology ◽  
2000 ◽  
Vol 2 (5) ◽  
pp. 501-506 ◽  
Author(s):  
Dalia Perelman ◽  
Nancy Lu
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Caenorhabditis Elegans ◽  
Branched Chain Amino Acids ◽  
Nematode Caenorhabditis Elegans ◽  
Optimal Range ◽  
C Elegans ◽  
Branched Chain Amino Acid ◽  
High Concentrations ◽  
Branched Chain

AbstractBranched chain amino acid (BCAA) requirements and their interactions were studied in the nematode Caenorhabditis elegans. Optimal, deficiency and toxic levels affecting nematode population growth were determined for each of the three BCAAs. The optimal range for leucine was 0.72-2.8; for isoleucine, 0.86-1.7; and for valine, 0.51-4.1 mg ml-1. Leucine at high concentrations was toxic. When isoleucine and valine were both added at high concentrations, they also exerted a marked toxic effect. The interactions of the branched chain amino acids found among vertebrate animals were not observed in C. elegans. Les besoins relatifs aux amino-acides en chaîne ramifiée et leurs interactions chez le nématode Caenorhabditis elegans - Les besoins relatifs aux amino-acides en chaîne ramifiée (BCAA) et leurs interactions ont été étudiés chez le nématode Caenorhabditis elegans. Les niveaux optimal, de déficience et toxique affectant la croissance de la population du nématode ont été déterminés pour chacune des BCAA. L'optimum est, pour la leucine de 0,72 à 2,8, pour l'isoleucine de 0,86 à 1,7 et pour la valine de 0,51 à 4,1 mg ml-1. A forte concentration la leucine est toxique. Si l'isoleucine et la valine sont ajoutées à forte concentration elles exercent également une action toxique prononcée. Les interactions entre BCAA observées chez les vertébrés ne l'ont pas été chez les C. elegans.

Neutrophil Elastase Potentiates Cathepsin G-lnduced Platelet Activation

1992 ◽  
Vol 68 (05) ◽  
pp. 570-576 ◽  
Author(s):  
Mary A Selak
Keyword(s):  
Neutrophil Elastase ◽  
Cell Activation ◽  
Thromboxane A2 ◽  
Creatine Phosphate ◽  
Dense Granule ◽  
Cathepsin G ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Low Concentrations ◽  
High Concentrations

SummaryWe have previously demonstrated that human neutrophil cathepsin G is a strong platelet agonist that binds to a specific receptor. This work describes the effect of neutrophil elastase on cathepsin G-induced platelet responses. While platelets were not activated by high concentrations of neutrophil elastase by itself, elastase enhanced aggregation, secretion and calcium mobilization induced by low concentrations of cathepsin G. Platelet aggregation and secretion were potentiated in a concentration-dependent manner by neutrophil elastase with maximal responses observable at 200 nM. Enhancement was observed when elastase was preincubated with platelets for time intervals of 10–60 s prior to addition of a low concentration of cathepsin G and required catalytically-active elastase since phenylmethanesulphonyl fluoride-inhibited enzyme failed to potentiate cell activation. Neutrophil elastase potentiation of platelet responses induced by low concentrations of cathepsin G was markedly inhibited by creatine phosphate/creatine phosphokinase and/or indomethacin, indicating that the synergism between elastase and cathepsin G required the participation of ADP and thromboxane A2. On the other hand, platelet responses were not attenuated by the PAF antagonist BN 52021, signifying that PAF-acether did not play a role in elastase potentiation. At higher concentrations porcine pancreatic elastase exhibits similar effects to neutrophil elastase, demonstrating that the effect of elastase was not unique to the neutrophil protease. While neutrophil elastase failed to alter the ability of cathepsin G to hydrolyze a synthetic chromogenic substrate, preincubation of platelets with elastase increased the apparent affinity of cathepsin G binding to platelets. In contrast to their effect on cathepsin G-induced platelet responses, neither neutrophil nor pancreatic elasatse potentiated aggregation or dense granule release initiated by ADP, PAF-acether, arachidonic acid or U46619, a thromboxane A2 mimetic. Moreover, unlike its effect on cathepsin G, neutrophil elastase inhibited thrombin-induced responses. The current observations demonstrate that elastase can potentiate platelet responses mediated by low concentrations of cathepsin G, suggesting that both enzymes may function synergistically to activate platelets under conditions where neutrophil degranulation occurs.

In Vitro Effects of Ethanol on Rabbit Platelet Aggregation, Secretion of Granule Contents, and Cyclic AMP Levels in the Presence of Prostacyclin

1989 ◽  
Vol 61 (02) ◽  
pp. 254-258 ◽  
Author(s):  
Margaret L Rand ◽  
Peter L Gross ◽  
Donna M Jakowec ◽  
Marian A Packham ◽  
J Fraser Mustard
Keyword(s):  
Cyclic Amp ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Inhibitory Effects ◽  
Low Concentrations ◽  
Rabbit Platelets ◽  
High Concentrations ◽  
In Vitro Effects ◽  
Aggregation Of Platelets

SummaryEthanol, at physiologically tolerable concentrations, inhibits platelet responses to low concentrations of collagen or thrombin, but does not inhibit responses of washed rabbit platelets stimulated with high concentrations of ADP, collagen, or thrombin. However, when platelet responses to high concentrations of collagen or thrombin had been partially inhibited by prostacyclin (PGI2), ethanol had additional inhibitory effects on aggregation and secretion. These effects were also observed with aspirin- treated platelets stimulated with thrombin. Ethanol had no further inhibitory effect on aggregation of platelets stimulated with ADP, or the combination of ADP and epinephrine. Thus, the inhibitory effects of ethanol on platelet responses in the presence of PGI2 were very similar to its inhibitory effects in the absence of PGI2, when platelets were stimulated with lower concentrations of collagen or thrombin. Ethanol did not appear to exert its inhibitory effects by increasing cyclic AMP above basal levels and the additional inhibitory effects of ethanol in the presence of PGI2 did not appear to be brought about by further increases in platelet cyclic AMP levels.

Aggregation of Cat Platelets in Vitro

1970 ◽  
Vol 23 (03) ◽  
pp. 601-620 ◽  
Author(s):  
Th. B Tschopp
Keyword(s):  
Adenosine Monophosphate ◽  
Blood Collection ◽  
Base Line ◽  
Reversible Aggregation ◽  
Low Concentrations ◽  
Irreversible Aggregation ◽  
High Concentrations ◽  
Two Phases ◽  
Improved Technique

SummaryAggregation of cat platelets in the citrated plasma is examined by means of Born’s absorptiometer. A marked tendency of the platelets of this species to spontaneous aggregation necessitated first of all the development of an improved technique of blood collection.A hypothesis according to which 5-HT is released from the platelets, explains the absence of oscillations on the base line of the absorptiometer, the absence of platelet swelling, when ADP is added, and the effect of stirring on the aggregation curves in cat PRP. The average volume of cat platelets amounts to 10.46 μ3 when directly fixed in the blood, when fixed from PRP to 12.17 μ3, when fixed from stirred PRP to 13.51 μ3.In low concentrations (0.3-2 μM) ADP produce reversible aggregation; in narrowly restricted, individually dissimilar mean concentrations irreversible aggregation in two phases and in high concentrations, irreversible aggregation in one phase. Like ADP serotonin produces 2 phase irreversible aggregation in concentrations of 3-10 μM, but unlike ADP, the aggregation velocity decreases again with high 5-HT concentrations (>100 μM). Adrenaline does not produce aggregation and it is likely that adenosine and adenosine monophosphate inhibit the aggregation by serotonin but not by ADP. Species differences in the aggregation of human, rabbit and cat platelets are discussed.

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