scholarly journals MCT4 is a high affinity transporter capable of exporting lactate in high-lactate environments

2019 ◽  
Author(s):  
Y Contreras-Baeza ◽  
PY Sandoval ◽  
R Alarcón ◽  
A Galaz ◽  
F Cortés-Molina ◽  
...  
Keyword(s):  
Metastatic Cancer ◽  
Hek293 Cells ◽  
Substrate Affinity ◽  
Kinetic Properties ◽  
Robust Property ◽  
Order Of Magnitude ◽  
Lactate Uptake ◽  
Warburg Phenomenon ◽  
Ph Probes ◽  
High Lactate

AbstractMCT4 is an H+-coupled transporter expressed in metastatic cancer cells, macrophages, and other highly glycolytic cells, where it extrudes excess lactate generated by the Warburg phenomenon or by hypoxia. Intriguingly, its reported Kmfor lactate, obtained with pH-sensitive probes, is more than an order of magnitude higher than physiological lactate. Here we examined MCT4-rich MDA-MB-231 cells using the FRET sensor Laconic and found a median Kmfor lactate uptake of only 1.7 mM, while parallel estimation in the same cells with a pH probe gave a Kmof 27 mM. The median Kmof MCT4 for lactate was 0.7 mM in MCT4-expressing HEK293 cells and 1.2 mM in human macrophages, suggesting that high substrate affinity is a robust property of the transporter. Probed with the FRET sensor Pyronic, MCT4 showed a Kmfor pyruvate of only 4.2 mM in MDA-MB-231 cells, as opposed to > 150 mM reported previously. We conclude that prior estimates of MCT4 affinity based on pH probes were severely biased by the confounding action of pH regulatory mechanisms. Numerical simulation showed that MCT4, but not MCT1 or MCT2, endows cells with the capability of lactate extrusion in high lactate environments. The revised kinetic properties and novel transport assays may help in developing small-molecule MCT4 blockers for research and therapy.

scholarly journals Leg and arm lactate and substrate kinetics during exercise

2003 ◽  
Vol 284 (1) ◽  
pp. E193-E205 ◽  
Author(s):  
G. van Hall ◽  
M. Jensen-Urstad ◽  
H. Rosdahl ◽  
H.-C. Holmberg ◽  
B. Saltin ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Muscle Mass ◽  
Lactate Concentration ◽  
Whole Body ◽  
Glucose Turnover ◽  
Lactate Oxidation ◽  
Arterial Lactate ◽  
Lactate Uptake ◽  
High Lactate

To study the role of muscle mass and muscle activity on lactate and energy kinetics during exercise, whole body and limb lactate, glucose, and fatty acid fluxes were determined in six elite cross-country skiers during roller-skiing for 40 min with the diagonal stride (Continuous Arm + Leg) followed by 10 min of double poling and diagonal stride at 72–76% maximal O2 uptake. A high lactate appearance rate (Ra, 184 ± 17 μmol · kg−1 · min−1) but a low arterial lactate concentration (∼2.5 mmol/l) were observed during Continuous Arm + Leg despite a substantial net lactate release by the arm of ∼2.1 mmol/min, which was balanced by a similar net lactate uptake by the leg. Whole body and limb lactate oxidation during Continuous Arm + Leg was ∼45% at rest and ∼95% of disappearance rate and limb lactate uptake, respectively. Limb lactate kinetics changed multiple times when exercise mode was changed. Whole body glucose and glycerol turnover was unchanged during the different skiing modes; however, limb net glucose uptake changed severalfold. In conclusion, the arterial lactate concentration can be maintained at a relatively low level despite high lactate Ra during exercise with a large muscle mass because of the large capacity of active skeletal muscle to take up lactate, which is tightly correlated with lactate delivery. The limb lactate uptake during exercise is oxidized at rates far above resting oxygen consumption, implying that lactate uptake and subsequent oxidation are also dependent on an elevated metabolic rate. The relative contribution of whole body and limb lactate oxidation is between 20 and 30% of total carbohydrate oxidation at rest and during exercise under the various conditions. Skeletal muscle can change its limb net glucose uptake severalfold within minutes, causing a redistribution of the available glucose because whole body glucose turnover was unchanged.

scholarly journals A Miniature pH Probe Using Functional Microfiber Bragg Grating

Optics ◽  
2020 ◽  
Vol 1 (2) ◽  
pp. 202-212 ◽  
Author(s):  
Yang Ran ◽  
Peng Xiao ◽  
Yongkang Zhang ◽  
Deming Hu ◽  
Zhiyuan Xu ◽  
...  
Keyword(s):  
Self Assembly ◽  
Ph Sensor ◽  
Fiber Surface ◽  
Bragg Grating ◽  
Wavelength Shift ◽  
Layer By Layer ◽  
Compact Size ◽  
Layer Technique ◽  
Order Of Magnitude ◽  
Ph Probes

Operando and precisely probing aqueous pH is fundamentally demanded, both in chemical and biological areas. Conventional pH probes, subjected to the larger size, are probably unfit for application in some extreme scenarios, such as a trace amount of samples. In this paper, we have further developed the pH sensor that leverages the microfiber Bragg grating with an ultra-compact size down to an order of magnitude of 10−14 m3. Using the electrostatic self-assembly layer-by-layer technique, the functional film consisting of sodium alginate, which harnesses a pH-dependent hygroscopicity, is immobilized on the fiber surface. Consequently, the alteration of aqueous pH could be quantitatively indicated by the wavelength shift of the grating resonance via the refractive index variation of the sensing film due to the water absorption or expulsion. The grating reflections involving fundamental mode and higher order mode exhibit the sensitivities of −72 pm/pH and −265 pm/pH, respectively. In addition, temperature compensation can be facilitated by the recording of the two reflections simultaneously. Furthermore, the modeling and simulation results predict the pivotal parameters of the configuration in sensitivity enhancement. The proposed proof-of-concept enriches the toolbox of pH sensor for catering to the need of detection in some extremely small spaces—for example, the living cells or the bio-tissues.

Regulation of Fructose 1,6-Bisphosphatase Activity of Chlorella by Mole Mass Change

1996 ◽  
Vol 51 (9-10) ◽  
pp. 639-645 ◽  
Author(s):  
N. Grotjohann
Keyword(s):  
Enzyme Regulation ◽  
Fold Increase ◽  
Substrate Affinity ◽  
Kinetic Properties ◽  
Enzyme Form ◽  
Phosphorylated Compounds ◽  
Fructose 1,6 Bisphosphatase ◽  
Chloroplast Stroma ◽  
Fructose 1,6 Bisphosphate

Fast protein liquid chromatography on Superose 6 of partially purified FBPase II from Chlorella reveals a 1350 kDa-form at pH 6.0 and a 67 kDa-form at pH 8.5. Treatment of the large enzyme form with 5mᴍ concentrations of Mg2+, F1,6P2, DTT or ATP leads to dissociation into smaller ones of 215 -470 kDa. Aggregation/dissoziation is a reversible process, as has been shown for the effect of F1,6P2 and of pH, by rechromatography. The change in mole mass results in alterations of the activitiy and of the kinetic properties of the enzyme forms, obtained. Dissociation results in a 4 - 6 fold increase in activity, as can be shown for F1,6P2-treated samples. Halfsaturation constants, as well as the degree of cooperativity of the 67- and the 1350- kDa form, are different for substrate affinity, activation by Mg2+ and DTT, and for inhibition by ATP. Both enzyme forms hydrolyse fructose 1,6 bisphosphate and seduheptulose 1,7 bisphosphate better than other phosphorylated compounds. The ratio of F1,6P2- to SDP-cleavage is 100:58 for the small enzyme form and 100: 84 for the large one. Activation of FBPase II in the light and inactivation in the dark is discussed on the basis of different oligomeric forms of the enzyme, generated by changes in the concentration of intermediates and effectors in the chloroplast stroma, leading to dissociation or aggregation. The conclusion is drawn that oligomerization of key enzymes, resulting in enzyme forms with different activities and different kinetic properties, might provide an effective mechanism for enzyme regulation in vivo

scholarly journals Isoform expression in the multiple soluble malate dehydrogenase of Hoplias malabaricus (Erythrinidae, Characiformes)

2003 ◽  
Vol 63 (1) ◽  
pp. 7-15 ◽  
Author(s):  
M. R. Aquino-Silva ◽  
M. L. B. Schwantes ◽  
A. R. Schwantes
Keyword(s):  
Skeletal Muscle ◽  
Malate Dehydrogenase ◽  
Tandem Duplication ◽  
Carbon Flow ◽  
Substrate Affinity ◽  
Kinetic Properties ◽  
Thermal Stabilities ◽  
Hoplias Malabaricus ◽  
Isoform Expression

Kinetic properties and thermal stabilities of Hoplias malabaricus liver and skeletal muscle unfractionated malate dehydrogenase (MDH, EC 1.1.1.37) and its isolated isoforms were analyzed to further study the possible sMDH-A* locus duplication evolved from a recent tandem duplication. Both A (A1 and A2) and B isoforms had similar optima pH (7.5-8.0). While Hoplias A isoform could not be characterized as thermostable, B could as thermolabile. A isoforms differed from B isoform in having higher Km values for oxaloacetate. The possibly duplicated A2 isoform showed higher substrate affinity than the A1. Hoplias duplicated A isoforms may influence the direction of carbon flow between glycolisis and gluconeogenesis.

scholarly journals Biochemical characterization of the catalytic domains of three different clostridial collagenases

2009 ◽  
Vol 390 (1) ◽  
Author(s):  
Ulrich Eckhard ◽  
Esther Schönauer ◽  
Paulina Ducka ◽  
Peter Briza ◽  
Dorota Nüss ◽  
...  
Keyword(s):  
Biochemical Characterization ◽  
Substrate Affinity ◽  
Catalytic Domains ◽  
Zinc Binding Site ◽  
N Terminus ◽  
Activation Mechanisms ◽  
Order Of Magnitude ◽  
Therapy And Diagnosis ◽  
Prime Target

Abstract Clostridial collagenases are used for a broad spectrum of biotechnological applications and represent prime target candidates for both therapy and diagnosis of clostridial infections. In this study, we biochemically characterized the catalytic domains of three clostridial collagenases, collagenase G (ColG) and H (ColH) from Clostridium histolyticum, and collagenase T (ColT) from C. tetani. All protein samples showed activity against a synthetic peptidic substrate (furylacryloyl-Leu-Gly-Pro-Ala, FALGPA) with ColH showing the highest overall activity and highest substrate affinity. Whereas the K m values of all three enzymes were within the same order of magnitude, the turnover rate k cat of ColG decreased 50- to 150-fold when compared to ColT and ColH. It is noteworthy that the protein N-terminus significantly impacts their substrate affinity and substrate turnover as well as their inhibition profile with 1,10-phenanthroline. These findings were complemented with the discovery of a strictly conserved double-glycine motif, positioned 28 amino acids upstream of the HEXXH zinc binding site, which is critical for enzymatic activity. These observations have consequences with respect to the topology of the N-terminus relative to the active site as well as possible activation mechanisms.

scholarly journals Substrate specificity and structure of human aminoadipate aminotransferase/kynurenine aminotransferase II

2008 ◽  
Vol 28 (4) ◽  
pp. 205-215 ◽  
Author(s):  
Qian Han ◽  
Tao Cai ◽  
Danilo A. Tagle ◽  
Howard Robinson ◽  
Jianyong Li
Keyword(s):  
Substrate Specificity ◽  
Catalytic Efficiency ◽  
Structural Basis ◽  
Substrate Affinity ◽  
Kinetic Properties ◽  
Amino Group ◽  
Kynurenine Aminotransferase ◽  
Broad Substrate Specificity ◽  
Systematic Assessment ◽  
The Brain

KAT (kynurenine aminotransferase) II is a primary enzyme in the brain for catalysing the transamination of kynurenine to KYNA (kynurenic acid). KYNA is the only known endogenous antagonist of the N-methyl-D-aspartate receptor. The enzyme also catalyses the transamination of aminoadipate to α-oxoadipate; therefore it was initially named AADAT (aminoadipate aminotransferase). As an endotoxin, aminoadipate influences various elements of glutamatergic neurotransmission and kills primary astrocytes in the brain. A number of studies dealing with the biochemical and functional characteristics of this enzyme exist in the literature, but a systematic assessment of KAT II addressing its substrate profile and kinetic properties has not been performed. The present study examines the biochemical and structural characterization of a human KAT II/AADAT. Substrate screening of human KAT II revealed that the enzyme has a very broad substrate specificity, is capable of catalysing the transamination of 16 out of 24 tested amino acids and could utilize all 16 tested α-oxo acids as amino-group acceptors. Kinetic analysis of human KAT II demonstrated its catalytic efficiency for individual amino-group donors and acceptors, providing information as to its preferred substrate affinity. Structural analysis of the human KAT II complex with α-oxoglutaric acid revealed a conformational change of an N-terminal fraction, residues 15–33, that is able to adapt to different substrate sizes, which provides a structural basis for its broad substrate specificity.

scholarly journals Structural and Mutagenic Analysis of Metallo-β-Lactamase IMP-18

2016 ◽  
Vol 60 (9) ◽  
pp. 5521-5526 ◽  
Author(s):  
Takamitsu Furuyama ◽  
Haruka Nonomura ◽  
Yoshikazu Ishii ◽  
Nancy D. Hanson ◽  
Akiko Shimizu-Ibuka
Keyword(s):  
Crystal Structure ◽  
Active Site ◽  
Kinetic Properties ◽  
Amino Acid Residues ◽  
Content Type ◽  
Zinc Metalloenzymes ◽  
Order Of Magnitude ◽  
Sandwich Configuration ◽  
The Relationship ◽  
Loop Conformation

ABSTRACTIMP-type metallo-β-lactamases (MBLs) are exogenous zinc metalloenzymes that hydrolyze a broad range of β-lactams, including carbapenems. Here we report the crystal structure of IMP-18, an MBL cloned fromPseudomonas aeruginosa, at 2.0-Å resolution. The overall structure of IMP-18 resembles that of IMP-1, with an αβ/βα “folded sandwich” configuration, but the loop that covers the active site has a distinct conformation. The relationship between IMP-18's loop conformation and its kinetic properties was investigated by replacing the amino acid residues that can affect the loop conformation (Lys44, Thr50, and Ile69) in IMP-18 with those occupying the corresponding positions in the well-described enzyme IMP-1. The replacement of Thr50 with Pro considerably modified IMP-18's kinetic properties, specifically those pertaining to meropenem, with thekcat/Kmvalue increased by an order of magnitude. The results indicate that this is a key residue that defines the kinetic properties of IMP-type β-lactamases.

Organ-specific regulation of phosphofructokinase during facultative anaerobiosis in the marine whelk Busycotypus canaliculatum

1991 ◽  
Vol 69 (1) ◽  
pp. 70-75 ◽  
Author(s):  
Ross E. Whitwam ◽  
Kenneth B. Storey
Keyword(s):  
Protein Kinase ◽  
Active Form ◽  
Covalent Modification ◽  
Retractor Muscle ◽  
Affinity Constant ◽  
Enzyme Analysis ◽  
Substrate Affinity ◽  
Kinetic Properties ◽  
Enzyme Form ◽  
Fructose 2

The kinetic properties of 6-phosphofructo-1-kinase (PFK) were assessed in five organs (ventricle, radular retractor muscle, gill, hepatopancreas, and kidney) of aerobic and anoxic (21 h in N2-bubbled seawater) whelks, Busycotypus canaliculatum. The enzyme in all organs showed a stable modification of kinetic parameters as a result of exposure of the animal to anoxic conditions. In most cases these changes were consistent with the conversion of the enzyme to a less active form in the anoxic organ. In ventricle, for example, the anoxic enzyme form showed significant changes, including a 36% increase in the value of the substrate affinity constant (S0.5) for Mg∙ATP, a 19% increase in S0.5 fructose-6-phosphate, a 57% increase in the 50% inhibition value (I50) for phosphoenolpyruvate, a 30% increase in I50 citrate, and a fivefold increase in the activator constant (Ka) for fructose-2, 6-bisphosphate, as compared with the aerobic enzyme. Analysis of the time course of anoxia-induced modification of PFK showed that changes to the properties of gill PFK were accomplished within 2 h of the exposure to N2-bubbled seawater, whereas changes to ventricle PFK required up to 8 h. In vitro incubation of ventricle homogenates with Mg∙ATP plus protein kinase second messengers or with Mg2+ plus added protein phosphatases showed that the aerobic enzyme form was modified by protein kinase action with an increase in Ka fructose-2,6-bisphosphate that mimicked the effect of the aerobic to anoxic transition on the enzyme. Phosphatase action on the anoxic enzyme form had the opposite effect. The data suggest that the modification of PFK properties under anoxia in whelk organs is due to protein phosphorylation of the enzyme. Such covalent modification of PFK and other enzymes, notably pyruvate kinase, coordinates the anoxia-induced glycolytic rate depression and overall metabolic arrest that is a prominent feature of facultative anaerobiosis in marine molluscs.

scholarly journals Cloning, Sequencing, and Expression of the Gene Encoding Cyclic 2,3-Diphosphoglycerate Synthetase, the Key Enzyme of Cyclic 2,3-Diphosphoglycerate Metabolism in Methanothermus fervidus

1998 ◽  
Vol 180 (22) ◽  
pp. 5997-6004 ◽  
Author(s):  
Karl Matussek ◽  
Patrick Moritz ◽  
Nina Brunner ◽  
Christoph Eckerskorn ◽  
Reinhard Hensel
Keyword(s):  
Substrate Affinity ◽  
Kinetic Properties ◽  
Gene Encoding ◽  
Enzyme Preparations ◽  
E Coli ◽  
Gene Coding ◽  
Key Enzyme ◽  
Methanothermus Fervidus ◽  
Synthetic Reaction ◽  
Sequencing And Expression

ABSTRACT Cyclic 2,3-diphosphoglycerate synthetase (cDPGS) catalyzes the synthesis of cyclic 2,3-diphosphoglycerate (cDPG) by formation of an intramolecular phosphoanhydride bond in 2,3-diphosphoglycerate. cDPG is known to be accumulated to high intracellular concentrations (>300 mM) as a putative thermoadapter in some hyperthermophilic methanogens. For the first time, we have purified active cDPGS from a methanogen, the hyperthermophilic archaeon Methanothermus fervidus, sequenced the coding gene, and expressed it in Escherichia coli. cDPGS purification resulted in enzyme preparations containing two isoforms differing in their electrophoretic mobility under denaturing conditions. Since both polypeptides showed the same N-terminal amino acid sequence and Southern analyses indicate the presence of only one gene coding for cDPGS in M. fervidus, the two polypeptides originate from the same gene but differ by a not yet identified modification. The native cDPGS represents a dimer with an apparent molecular mass of 112 kDa and catalyzes the reversible formation of the intramolecular phosphoanhydride bond at the expense of ATP. The enzyme shows a clear preference for the synthetic reaction: the substrate affinity and the V max of the synthetic reaction are a factor of 8 to 10 higher than the corresponding values for the reverse reaction. Comparison with the kinetic properties of the electrophoretically homogeneous, apparently unmodified recombinant enzyme from E. coli revealed a twofold-higher V max of the enzyme from M. fervidus in the synthesizing direction.

Abstract 376: Nedd4 Regulated Bk Channels in Diabetes Mellitus

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
DAI-MIN ZHANG ◽  
Shao-liang Chen ◽  
Yanrong Zhu ◽  
Peng Ye
Keyword(s):  
Diabetes Mellitus ◽  
Current Density ◽  
Knockout Mice ◽  
Vascular Function ◽  
Critical Role ◽  
Vascular Diseases ◽  
Bk Channels ◽  
Bk Channel ◽  
Hek293 Cells ◽  
Kinetic Properties

Big conductance calcium activated potassium(BK) channel plays a critical role in pathophysiological regulation of vascular function. Recent studies indicated that the expression reduction of BK channels in high glucose condition exacerbated vessel dilation, and led to coronary artery diseases, while BK channel expression was reserved in A-kinase anchoring protein(AKAP) knockout mice at same condition. Here, We are to investigate heterologous co-expression of Nedd4 ligase, ubiquitin protein ligase, and KCa1.1 in HEK293 cells. The result shown that co-expression reduced BK current density without modulation of kinetic properties as measured by path clamp techniques. Modulation of current density was dependent on ligase activity and was lost in AKAP knockout mice with diabetes mellitus. Taken together, our data disclose a novel mechanism of KCa1.1 channel regulation that NEDD4 decreased BK channels expression in diabetes mellitus depending on AKAP signal complexity. These findings provide a new insight into potential therapeutic target in vascular diseases, especially in diabetes mellitus.This work was supported by the National Natural Science Foundation of China(Grant No. 8137034)

Sign in / Sign up

Export Citation Format

Share Document