A kinetic study of pig liver pyruvate kinase activated by fructose diphosphate.
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ABSTRACT:
SUBMITTER: Macfarlane N
PROVIDER: S-EPMC1166314 | biostudies-other | 1974 Jun
REPOSITORIES: biostudies-other
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Project description:The paper reports a study of the kinetics of the reaction between phosphoenolpyruvate, ADP and Mg(2+) catalysed by yeast pyruvate kinase when activated by fructose 1,6-diphosphate and K(+). The experimental results indicate that the reaction mechanism is of the Ordered Tri Bi type with the substrates binding in the order phosphoenolpyruvate, ADP and Mg(2+). Direct phosphoryl transfer takes place in the quaternary complex, with pyruvate released before MgATP. A dead-end enzyme-pyruvate complex is also indicated. Values have been determined for the Michaelis, dissociation and inhibition constants of the reaction. Several of the rate constants involved have also been evaluated.
| S-EPMC1174261 | biostudies-other
Project description:Preparation of the L form of rabbit liver pyruvate kinase (EC 2.7.1.40) in the presence of fructose 1,6-diphosphate yielded an enzyme which was kinetically identical with the M or muscle-type form of pyruvate kinase found in liver. Chromatographic and dialysis studies of this complex showed that most of the fructose 1,6-diphosphate molecules were loosely bound to the enzyme, but dilution-dissociation studies and binding experiments established that there was a high initial affinity between the enzyme and fructose 1,6-diphosphate (K(assoc.)=2.3x10(9)), and that binding of the loosely bound fructose 1,6-diphosphate was concentration-dependent and a necessary condition to overcome the co-operative interaction observed with the homotropic effector phosphoenolpyruvate. Preparation of the liver enzyme in the absence of EDTA did not yield a predominantly M form of the enzyme, and incubation of the M form in the presence of EDTA did not convert it into the L form, but resulted in inhibition of enzyme activity. Immunological studies confirmed that the L and M forms in liver were distinct, and that preparation of the L form in the presence of fructose 1,6-diphosphate did not produce an enzyme antigenically different from the L form prepared in the absence of this heterotropic effector.
| S-EPMC1177470 | biostudies-other
Project description:1. An investigation of the reaction mechanism of the fructose 1,6-bisphosphate-activated pyruvate kinase isolated from the hepatopancreas of the crab Carcinus maenas was conducted. The enzyme was assayed in the presence of 500 microns-fructose 1,6-bisphosphate, 75 mM-KCl and 8 mM-Mg2+free at 25 degrees C. The results are consistent with a rapid-equilibrium random mechanism. 2. Evidence is presented that suggests the formation of two mixed-substrate-product dead-end complexes, enzyme-ADP-pyruvate and enzyme-ADP-ATP. 3. Competitive substrate inhibition was observed for both substrates, ADP and phosphoenolpyruvate, suggesting the formation of the complexes enzyme-ADP-ADP and enzyme-phosphoenolpyruvate-phosphoenolpyruvate in the suggested mechanism. 4. Data from the ATP product-inhibition studies indicate the formation of the complex enzyme-ATP-ATP. This suggests that in the reverse reaction ATP also will show substrate inhibition. 5. The presence of a saturating concentration of fructose 1,6-bisphosphate does not cause full activation of the purified preparations of the enzyme. 6. Pyruvate kinase activity in the supernatant of a hepatopancreas homogenate was completely activated by fructose 1,6-bisphosphate, suggesting that the binding of this ligand to the purified pyruvate kinase was impaired.
| S-EPMC1161355 | biostudies-other
Project description:1. Kinetics of fructose 1,6-diphosphate activation of liver pyruvate kinase type I inhibited with MgATP and l-alanine are described as a function of enzyme and fructose 1,6-diphosphate concentrations. These results can be explained by a single pseudo-first-order transition of the enzyme into an active form, independent of the enzyme concentration. This rate constant, k(app.)=0.24s(-1) with 0.02mm-fructose 1,6-diphosphate (t(0.9) approximately 10s where t(0.9) is the time for 90% conversion), is an increasing function of fructose 1,6-diphosphate concentration far beyond that needed to maximally activate enzyme equilibrated with fructose 1,6-diphosphate (about 20mum). 2. The model equations are best analysed with numerical techniques which are described. These techniques are useful in studying similar slow transients frequently observed in stopped-flow studies of enzymes. 3. Shorter transients (t(0.9)=0.5-1.5s) were observed in the kinetic response of the enzyme to the addition of MgATP or phosphoenolpyruvate, but were not further characterized.
| S-EPMC1168056 | biostudies-other
Project description:The allosteric regulation of human liver pyruvate kinase (hL-PYK) by fructose-1,6-bisphosphate (Fru-1,6-BP; activator), ATP (inhibitor) and alanine (Ala; inhibitor) was monitored over a pH range from 6.5 to 8.0 at 37 degrees C. As a function of increasing pH, hL-PYK's affinity for the substrate phosphoenolpyruvate (PEP), and for Fru-1,6-BP decreases, while affinities for ATP and alanine slightly increases. At pH 6.5, Fru-1,6-BP and ATP elicit only small allosteric impacts on PEP affinity. As pH increases, Fru-1,6-BP and ATP elicit greater allosteric responses, but the response to alanine is relatively constant. Since the magnitudes of the allosteric coupling for ATP and for alanine inhibition are different and the pH dependences of these magnitudes are not similar, these inhibitors likely elicit their responses using different molecular mechanisms. In addition, our results fail to support a general correlation between pH dependent changes in effector affinity and pH dependent changes in the corresponding allosteric response.
| S-EPMC2687410 | biostudies-literature
Project description:In the study of allosteric proteins, understanding which effector-protein interactions contribute to allosteric activation is important both for designing allosteric drugs and for understanding allosteric mechanisms. The antihyperglycemic target, human liver pyruvate kinase (hL-PYK), binds its allosteric activator, fructose 1,6-bisphosphate (Fru-1,6-BP), such that the 1'-phosphate interacts with side chains of Arg501 and Trp494 and the 6'-phosphate interacts with Thr444, Thr446, Ser449 (i.e., the 444-449 loop), and Ser531. Additionally, backbone atoms from the 527-533 loop interact with a sugar ring hydroxyl and the two effector phosphate moieties. An effector analogue series indicates that only one phosphate on the sugar is required for activation. However, singly phosphorylated sugars, including Fru-1-P and Fru-6-P, bind with a Kix in the range of 0.07-1 mM. The second phosphate of Fru-1,6-BP causes tight effector binding, because this native effector has a Kix of 0.061 μM. Glucose 1,6-bisphosphate and ribulose 1,5-bisphosphate bind in the 0.07-1 mM range. The contrast with a higher Fru-1,6-BP binding indicates specificity for the fructose sugar conformation. Site-directed random mutagenesis at each residue that contacts bound Fru-1,6-BP showed that a negative charge introduced at position 531 mimics allosteric activation, even in the absence of Fru-1,6-BP. Collectively, analogue and mutagenesis studies are consistent with the 527-533 loop playing a key role in allosteric function. Deletion mutations that shortened the 527-533 loop were expected to prevent formation of hydrogen bonds between backbone atoms on the loop and Fru-1,6-BP. Indeed, Fru-1,6-BP did not activate these loop-shortened mutant proteins. Previous structural comparisons of M1-PYK and M2-PYK indicate that the 527-533 loop makes interactions across a subunit interface when an activator is not present. Mutating the hL-PYK subunit interface interactions among Trp527, Arg528, and Asp499 mimics allosteric activation. Considered with published structures, these results are consistent with (1) the two phosphates of Fru-1,6-BP docking to Arg501/Trp494 and the 444-449 loop, respectively, and (2) the formation of hydrogen bonds among Fru-1,6-BP and backbone atoms of the 527-533 loop pulling this loop away from the subunit interface, which results in breaking of the Trp527-Arg528-Asp499 interactions to elicit an allosteric response.
| S-EPMC5286843 | biostudies-literature
Project description:During analysis of pyruvate kinase distribution in developing guinea-pig liver it was observed that a substantial proportion of the activity remained associated with the microsomal membrane fraction ('microsomes'). Although some of this could be removed by washing with sucrose, the majority required detergent treatment for liberation, and even then at least one-half remained attached to the microsomes. Estimates of the contribution of this fraction to total cell pyruvate kinase activity indicated that it was more than 50% of the total, and this is likely to be an underestimate because of the continued latency of the enzyme even in the presence of detergent. The susceptibility of the microsomal enzyme, whether released by detergent or sucrose washing, to inactivation by Triton X-100 suggested it to be different from the cytosolic enzyme, which was stable under such conditions. (The microsomal enzyme required the presence of additional protein, such as bovine serum albumin, to maintain stability.) This view was confirmed by DEAE-cellulose chromatography and particularly isoelectric focusing, where the microsomal enzyme was shown to consist of at least four forms, which were distinctly different from those in the cytosol. Those data and the kinetic properties of the four forms in the membrane fraction indicate that the microsomal pyruvate kinase could consist of four counterparts to the cytosolic isoenzyme forms. These results are discussed in relation to the two possible explanations for the phenomenon (not mutually exclusive): that the more hydrophobic membrane forms are precursors of the cytosolic enzyme and that they may be part of functional glycolytic pathway in the microsomes of developing liver.
| S-EPMC1146655 | biostudies-other
Project description:The paper reports a study of the kinetics of the reaction between phosphoenolpyruvate, ADP and Mg(2+) catalysed by rabbit muscle pyruvate kinase. The experimental results indicate that the reaction mechanism is equilibrium random-order in type, that the substrates and products are phosphoenolpyruvate, ADP, Mg(2+), pyruvate and MgATP, and that dead-end complexes, between pyruvate, ADP and Mg(2+), form randomly and exist in equilibrium with themselves and other substrate complexes. Values were determined for the Michaelis, dissociation and inhibition constants of the reaction and are compared with values ascertained by previous workers.
| S-EPMC1177461 | biostudies-other
Project description:1. Preincubation of partially purified rat liver L-type pyruvate kinase at 25 degrees for 10min. causes a marked increase in co-operativity with respect to both the substrate, phosphoenolpyruvate, and the allosteric activator, fructose 1,6-diphosphate. 2. The results are consistent with the existence of two forms of liver L-type pyruvate kinase, designated forms L(A) and L(B). It is postulated that form L(A) has a low K(m) for phosphoenolpyruvate (about 0.1mm) and is not allosterically activated, whereas form L(B) is allosterically activated by fructose 1,6-diphosphate, exhibiting in the absence of the activator sigmoidal kinetics with half-maximal activity at about 1mm-phosphoenolpyruvate. In the presence of fructose 1,6-diphosphate, form L(B) gives Michaelis-Menten kinetics with K(m) less than 0.1mm. It is further postulated that preincubation converts form L(A) into form L(B). 3. The influence of pH on the preincubation effect was studied. 4. The inhibition of pyruvate kinase by Cu(2+) was studied in detail. Though phosphoenolpyruvate and fructose 1,6-diphosphate readily protect the enzyme against Cu(2+) inhibition, little evidence of significant reversal of the inhibition by these compounds could be found. 5. The effects of starvation, fructose feeding and preincubation on the pyruvate kinase activity of crude homogenates of various tissues of the rat were also studied.
| S-EPMC1198828 | biostudies-other
Project description:Two kinetically distinct forms of pyruvate kinase (EC 2.7.1.40) were isolated from rabbit liver by using differential ammonium sulphate fractionation. The L or liver form, which is allosterically activated by fructose 1,6-diphosphate, was partially purified by DEAE-cellulose chromatography to give a maximum specific activity of 20 units/mg. The L form was allosterically activated by K(+) and optimum activity was recorded with 30mm-K(+), 4mm-MgADP(-), with a MgADP(-)/ADP(2-) ratio of 50:1, but inhibition occurred with K(+) concentrations in excess of 60mm. No inhibition occurred with either ATP or GTP when excess of Mg(2+) was added to counteract chelation by these ligands. Alanine (2.5mm) caused 50% inhibition at low concentrations of phosphoenolpyruvate (0.15mm). The homotropic effector, phosphoenolpyruvate, exhibited a complex allosteric pattern (n(H)=2.5), and negative co-operative interactions were observed in the presence of low concentrations of this substrate. The degree of this co-operative interaction was pH-dependent, with the Hill coefficient increasing from 1.1 to 3.2 as the pH was raised from 6.5 to 8.0. Fructose 1,6-diphosphate interfered with the activation by univalent ions, markedly decreased the apparent K(m) for phosphoenolpyruvate from 1.2mm to 0.2mm, and transformed the phosphoenolpyruvate saturation curve into a hyperbola. Concentrations of fructose 1,6-diphosphate in excess of 0.5mm inhibited this stimulated reaction. The M or muscle-type form of the enzyme was not activated by fructose 1,6-diphosphate and gave a maximum specific activity of 0.3 unit/mg. A Michaelis-Menten response was obtained when phosphoenolpyruvate was the variable substrate (K(m)=0.125mm), and this form was inhibited by ATP, as well as alanine, even in the presence of excess of Mg(2+).
| S-EPMC1177469 | biostudies-other