Magnesium, Potassium, and the Adenylate Kinase Equilibrium

Blair, J. McD.

doi:10.1111/j.1432-1033.1970.tb00940.x

Cited by 98 publications

(27 citation statements)

References 26 publications

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“…To discuss this question, we consider the primary biochemical function of AK, to rapidly equilibrate ATP⅐Mg, AMP, ADP⅐Mg, and ADP. The [ATP]/ [ADP] ratio in its general form has long been recognized as an important parameter in energy regulation in cells (62,63 (68). Because magnesium is required in many biochemical processes and is generally well regulated (69), Blair further hypothesized that the regulatory role that magnesium ion play through AK is during the transient response of a cell's energy state (68).…”

Section: Resultsmentioning

confidence: 99%

Direct Mg2+ Binding Activates Adenylate Kinase from Escherichia coli

Tan

Hanson

Yang

2009

Journal of Biological Chemistry

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We report evidence that adenylate kinase (AK) from Escherichia coli can be activated by the direct binding of a magnesium ion to the enzyme, in addition to ATP-complexed Mg 2؉ . By systematically varying the concentrations of AMP, ATP, and magnesium in kinetic experiments, we found that the apparent substrate inhibition of AK, formerly attributed to AMP, was suppressed at low magnesium concentrations and enhanced at high magnesium concentrations. This previously unreported magnesium dependence can be accounted for by a modified random bi-bi model in which Mg 2؉ can bind to AK directly prior to AMP binding. A new kinetic model is proposed to replace the conventional random bi-bi mechanism with substrate inhibition and is able to describe the kinetic data over a physiologically relevant range of magnesium concentrations. According to this model, the magnesium-activated AK exhibits a 23-؎ 3-fold increase in its forward reaction rate compared with the unactivated form. The findings imply that Mg 2؉ could be an important affecter in the energy signaling network in cells. Adenylate kinase (AK)2 is a ϳ24-kDa enzyme involved in cellular metabolism that catalyzes the reversible phosphoryl transfer reaction (1) as in Reaction 1.It is recognized to play an important role in cellular energetic signaling networks (2, 3). A deficiency in human AK function may lead to such illness as hemolytic anemia (4 -8) and coronary artery disease (9); the latter is thought to be caused by a disruption of the AMP signaling network of AK (10). The ubiquity of AK makes it an ideal candidate for investigating evolutionary divergence and natural adaptation at a molecular level (11,12). Indeed, extensive structure-function studies have been carried out for AK (reviewed in Ref. 13). Both structural and biophysical studies have suggested that large-amplitude conformational changes in AK are important for catalysis (14 -19). More recently, the functional roles of conformational dynamics have been investigated using NMR (20 -22), computer simulations (23-27), and single-molecule spectroscopy (28). Given the critical role of AK in regulating cellular energy networks and its use as a model system for understanding the functional roles of conformational changes in enzymes, it is imperative that the enzymatic mechanism of AK be thoroughly characterized and understood.The enzymatic reaction of adenylate kinase has been shown to follow a random bi-bi mechanism using isotope exchange experiments (29). Isoforms of adenylate kinases characterized from a wide range of species have a high degree of sequence, structure, and functional conservation. Although all AKs appear to follow the same random bi-bi mechanistic framework (15, 29 -33), a detailed kinetic analysis reveals interesting variations among different isoforms. For example, one of the most puzzling discrepancies is the change in turnover rates with increasing AMP concentration between rabbit muscle AK and Escherichia coli AK. Although the reactivity of rabbit muscle AK is slightly inhibited at high...

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Section: Resultsmentioning

confidence: 99%

Direct Mg2+ Binding Activates Adenylate Kinase from Escherichia coli

Tan

Hanson

Yang

2009

Journal of Biological Chemistry

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“…The values used for the Mg-complex dissociation constants were chosen as follows. For MgATP, a series of experiments similar to those described by Blair [20] and de Weer and Lowe [21] have been carried out in this laboratory for the conditions used in most of the present experiments, namely ionic strength 0.15 M, 25 "C. The constant (0.025 mM) was close to the value obtained by Blair [20]. For Mg-3-P-glycerate, the value was extrapolated from several available results, none of which were carried out in exactly the present conditions [ 19,221.…”

Section: Experimen T A1 Conditionsmentioning

confidence: 99%

The Steady‐State Kinetics of Yeast Phosphoglycerate Kinase

Scopes¹

1978

European Journal of Biochemistry

101

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1.A re-investigation of the kinetics of yeast phosphoglycerate kinase in the direction of 1,3-bisphosphoglycerate formation has been carried out, covering a 1000-fold range in substrate concentrations. A variety of improved spectrophotometric and fluorimetric assay procedures have been used.2. Kinetic plots proved to be non-linear for each variable substrate. A variety of checks have been carried out to show that this is not due to artifacts in the assay procedures or heterogeneity of the enzyme preparation.3. The effects of a variety of salts on the activity of the enzyme have been examined. Most salts, especially those with multivalent anions, can cause activation of the enzyme, but inhibit at high concentration.4. The salt effect is shown to be principally due to anions rather than cations, and not to ionic strength changes. Sulphate, as one of the most effective anions has been used in most comparisons. 5. Salt activation is steepest when the substrate concentrations are low ; maximum activation has been about 5-fold with 0.2 mM MgATP and 0.2 mM 3-phosphoglycerate. Inhibition at the higher salt concentrations is strongest at the same substrate concentrations as when activation is steepest, indicating a link between the two effects.6. The presence of 20 mM or more Na2S04 converted non-linear kinetic plots to linear ones.

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“…The stability constants for the various complexes as published by O'Sullivan et al [21,22,25], Noat et al [23], and Blair [24] were used. The procedure was incorporated into a Fortran V program for use with a Univac-I 100 computer.…”

Section: Theoretical Calculationsmentioning

confidence: 99%

Improved Purification and Further Characterization of Acetyl‐CoA Carboxylase from Cultured Cells of Parsley (Petroselinum hortense)

Egin‐Bühler

Ebel

1983

European Journal of Biochemistry

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Acetyl-CoA carboxylase from irradiated cell-suspension cultures of parsley (Petroselinum hortense) has been purified to apparent homogeneity. The procedure included affinity chromatography of the enzyme on avidinmonomer -Sepharose 4B. Molecular weights of about 420000 for the native enzyme and about 220000 for the enzyme subunit were determined respectively by gel filtration or sucrose-density-gradient sedimentation and by electrophoresis in the presence of dodecyl sulfate. The purified enzyme showed an isoelectric point of 5.The enzyme carboxylated the straight-chain acyl-CoA esters of acetate, propionate, and butyrate at decreasing rates in this order. The catalytic efficiency of the carboxylase was highest when ATP existed largely as MgATP2-complex. At the optimum pH of 8 the apparent K, values for the substrates were: acetyl-CoA, 0.15mmol/l; bicarbonate, 1 mmol/l; MgATP2-, 0.07mmol/l. The carboxylase was inhibited by > 50mmol/l NaC1, KCl, or Tris/HCl buffer. The putative allosteric activator, citrate, stimulated the enzyme only slightly at concentrations below 2 mmol/l, but strongly inhibited the carboxylase at higher concentrations.The results of these studies demonstrate that several properties of the light-inducible acetyl-CoA carboxylase of parsley cells, an enzyme of the flavonoid pathway, are remarkably similar to those of acetyl-CoA carboxylases from a variety of other organisms. [l, 3,41. In suspension-cultured cells of parsley (Petroselinum hormwe), malonyl-CoA is required for two types of reaction in flavonoid biosynthesis, the formation of the aromatic ring A and the malonylation of the sugar moieties of flavonoid glycosides (Fig.

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Magnesium, Potassium, and the Adenylate Kinase Equilibrium

Cited by 98 publications

References 26 publications

Direct Mg2+ Binding Activates Adenylate Kinase from Escherichia coli

Direct Mg2+ Binding Activates Adenylate Kinase from Escherichia coli

The Steady‐State Kinetics of Yeast Phosphoglycerate Kinase

Improved Purification and Further Characterization of Acetyl‐CoA Carboxylase from Cultured Cells of Parsley (Petroselinum hortense)

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