Pyruvate kinase isozymes of Mucor racemosus: control of synthesis by glucose.

A variety of cultural conditions were examined to determine the relationship between pyruvate kinase isozyme patterns and morphology in Mucor racemosus. The results indicate that M. racemosus has two isozymes of pyruvate kinase, form A and form B, which are clearly separable on ion-exchange columns (diethylaminoethyl-cellulose). Addition of glucose to cultures growing on amino acids in air resulted in the induction of form A and the termination of form B synthesis. Cycloheximide added at the same time as glucose blocked the formation of form A but did not interfere with the termination of form B synthesis. Removal of glucose resulted in termination of form A synthesis and the induction of form B. Cycloheximide blocked the induction of form B and did not interfere with the termination of form A synthesis. The data show that the isozyme type is not directly related to morphology, but depends only on the presence or absence of glucose.     

Purification and characterization of a developmentally regulated carboxypeptidase from Mucor racemosus.

A developmentally regulated carboxypeptidase was purified from hyphae of the dimorphic fungus Mucor racemosus. The enzyme, designated carboxypeptidase 3 (CP3), has been purified greater than 900-fold to homogeneity and characterized. The carboxypeptidase migrated as a single electrophoretic band in isoelectric focusing polyacrylamide gel electrophoresis (PAGE), with an isoelectric point of pH 4.4. The apparent molecular mass of the native enzyme was estimated by gel filtration to be 52 kDa. Sodium dodecyl sulfate (SDS)-PAGE under nonreducing conditions revealed the presence of a single polypeptide of 51 kDa. SDS-PAGE of CP3 reacted with 2-mercaptoethanol revealed the presence of two polypeptides of 31 and 18 kDa, indicating a dimer structure (alpha 1 beta 1) of the enzyme with disulfide-linked subunits. By using [1,3-3H]diisopropylfluorophosphate as an active-site labeling reagent, it was determined that the catalytic site resides on the small subunit of the carboxypeptidase. With N-carboben zoxy-L-phenylalanyl-L-leucine (N-CBZ-Phe-Leu) as the substrate, the Km, kcat, and Vmax values were 1.7 x 10(-4) M, 490 s-1, and 588 mumol of Leu released per min per mg of protein, respectively. CP3 was determined to be a serine protease, since its catalytic activity was blocked by the serine protease inhibitors diisopropylfluorophosphate, phenylmethylsulfonyl fluoride, and 3,4-dichloroi Socoumarin (DCI). The enzyme was strongly inhibited by the mercurial compound p-chloromercuribenzoate. The carboxypeptidase readily hydrolyzed peptides with aliphatic or aromatic side chains, whereas most of the peptides which contained glycine in the penultimate position did not serve as substrates for the enzyme. Although CP3 activity was undetectable in Mucor yeast cells, antisera revealed the presence of the enzyme in the yeast form of the fungus. The partial amino acid sequence of the carboxypeptidase was determined.     

Purification and properties of pyruvate kinase from Streptococcus mutans.

Pyruvate kinase (EC 2.7.1.40) from Streptococcus mutans strain JC2 was purified, giving a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of the native enzyme was 180,000 to 190,000, and the enzyme was considered to consist of four identical subunits. This enzyme was completely dependent on glucose 6-phosphate for activity, and the saturation curve for activation by glucose 6-phosphate was sigmoidal. In the presence of 0.5 mM glucose 6-phosphate, the saturation curves for the substrates phosphoenolpyruvate and ADP were hyperbolic, and the Km values were 0.22 and 0.39 mM, respectively. GDP, IDP, and UDP could replace ADP, and the Km for GDP (0.026 mM) was 0.067 of that for ADP. The enzyme required not only divalent cations, Mg2+ or Mn2+, but also monovalent cations, K+ or NH4+, for activity, and it was strongly inhibited by Pi. When the concentration of Pi was increased, the half-saturating concentration and Hill coefficient for glucose 6-phosphate increased. However, the enzyme was immediately inactivated in a solution without Pi. The intracellular concentration of glucose 6-phosphate, in cooperation with that of Pi, may regulate pyruvate kinase activity in S. mutans.     

Purification and kinetic properties of pyruvate kinase from Brochothrix thermosphacta.

Pyravate kinase (ATP: pyruvate 2-0 phosphotransferase E.C.2.7.1.40) was purified from Brochothrix thermosphacta. The enzyme is a homotetramer of monomer Mr 58,000. Fructose-1,6-bisphosphate stimulates activity and promotes hyperbolic kinetics although it is not essential for enzyme activity. The positive effect of fructose-1,6-bisphosphate on activity is repressed by inorganic phosphate which enhances cooperative kinetics. Unlike pyruvate kinases from other sources, the Brochothrix enzyme is uncompetitively inhibited by glucose-6-phosphate, although at high concentration. ATP is a strong inhibitor of pyruvate kinase and shifts the residual activity/pH profile towards more alkaline values.     

Purification of a soluble and a wall-bound form of beta-glucosidase from Mucor racemosus.

beta-Glucosidase activity in crude extracts of Mucor racemosus exists in a soluble form and in a wall-bound form which sediments at 3,500 x g. The soluble form and a wall-bound form were purified to homogeneity by ammonium sulfate fractionation. DEAE-Sephadex chromatography, and SP-Sephadex chromatography. Both forms were identical in all parameters measured. Each enzyme is a glycoprotein of 91,000 daltons, with an identical amino acid composition and N-terminal amino acid of lysine; both contain about 10% carbohydrate. Both forms catalyze the hydrolysis of cellobiose and p-nitrophenyl-beta-D-glucoside with identical kinetic constants.     

Purification and regulatory properties of pyruvate kinase from Veillonella parvula.

The nonglycolytic, anaerobic organism Veillonella parvula M4 has been shown to contain an active pyruvate kinase. The enzyme was purified 126-fold and was shown by disc-gel electrophoresis to contain only two faint contaminating bands. The purified enzyme had a pH optimum of 7.0 in the forward direction and exhibited sigmoidal kinetics at varying concentrations o-f phosphoenol pyruvate (PEP), adenosine 5'-monophosphate (AMP), and Mg-2+ ions with S0.5 values of 1.5, 2.0, and 2.4 mM, respectively. Substrate inhibition was observed above 4 m PEP. Hill plots gave slope values (n) of 4.4 (PEP), 2.8 (adenosine 5'-diphosphate), and 2.0 (Mg-2+), indicating a high degree of cooperativity. The enzyme was inhibited non-competitively by adenosine 5'-triphosphate (Ki = 3.4 mM), and this inhibition was only slightly affected by increasing concentration of Mg-2+ ions to 30 mM. Competitive inhibition was observed with 3-phosphoglycerate, malate, and 2,3-diphosphoglycerate but only at higher inhibitor concentrations. The enzyme was activated by glucose-6-phosphate (P), fructose-6-P, fructose-1,6-diphosphate (P2), dihydroxyacetone-P, and AMP; the Hill coefficients were 2.2, 1.8, 1.5, 2.1, and 2.0, respectively. The presence of each these metabolites caused substrate velocity curves to change from sigmoidal to hyperbolic curves, and each was accompanied by an increase in the maximum activity, e.g., AMP greater than fructose-1,6-P2 greater than dihydroxyacetone-P greater than glucose-6-P greater than fructose-6-P. The activation constants for fructose-1,6-P2, AMP, and glucose-6-P were 0.3, 1.1, and 5.3 mM, respectively. The effect of 5 mM fructose-1,6-P2 was significantly different from the other compounds in that this metabolite was inhibitory between 1.2 and 3 mM PEP. Above this concentration, fructose-1,6-P2 activated the enzyme and abolished substrate inhibition by PEP. The enzyme was not affected by glucose, glyceraldehyde-3-P, 2-phosphoglycerate, lactate, malate, fumerate, succinate, and cyclic AMP. The results suggest that the pyruvate kinase from V. parvula M4 plays a central role in the control of gluconeogenesis in this organism by regulating the concentration of PEP.     

Purification and properties of pyruvate kinase from Bacillus stearothermophilus

Pyruvate kinase was purified to homogeneity from a moderate thermophile, Bacillus stearothermophilus. The molecular weight of the enzyme was found to be 250,000 on gel filtration and 242,000 on sedimentation analysis. The enzyme consisted of four identical subunits of a molecular weight of 62,000-64,000. There were no remarkable differences between the thermophilic enzyme and mesophilic enzymes in amino acid composition, secondary structure, mono- and di-valent cation requirements for activity or specificity for nucleoside diphosphates. But the thermophilic enzyme was stable at high temperature and for a longer period of storage at lower temperature. Its specific activity was relatively high even at a low temperature (30 degrees C). The enzyme exhibited homotropic positive cooperativity for phosphoenol-pyruvate, but not for ADP. It was allosterically activated by AMP, ribose 5-phosphate and nucleoside monophosphates, but not by fructose 1,6-bisphosphate. Activation by AMP and ribose 5-phosphate, and inhibition by inorganic phosphate were also observed even at the physiological temperature (60 degrees C) for the thermophile.     

Purification and properties of pyruvate kinase from Mycobacterium smegmatis

Pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from Mycobacterium smegmatis has been purified to homogeneity through a seven-step procedure with a yield of 16% and specific activity of 220 units/mg protein. The purified enzyme had a molecular weight of 230,700 and was composed of four subunits with identical molecular weights of 57,540. Analysis of amino acid composition revealed a low content of aromatic amino acids. The enzyme exhibited sigmoidal kinetics of varying concentrations of phosphoenolpyruvate, the degree of cooperativity and S_0.5v value for phosphoenolpyruvate being strongly dependent on the pH of the reaction mixture. Among the nucleoside diphosphates acting as substrate for pyruvate kinase, ADP was the best phosphate acceptor, as judged by its lowest K_m value. The enzyme showed an absolute requirement for divalent cations (either Mg²⁺ or Mn²⁺), but monovalent cations were not necessary for activity. Other divalent cations inhibited the Mg²⁺-activated enzyme to varying degrees (Ni²⁺ > Zn²⁺ > Cu²⁺ > Ca²⁺ > Ba²⁺). The differences in the kinetic responses of the enzyme to Mg²⁺ and Mn²⁺ are discussed.     

Purification and properties of pyruvate kinase from Dictyostelium discoideum

Pyruvate kinase (EC 2.7.1.40) from aggregating Dictyostelium discoideum cells has been purified to homogeneity. It has a monomeric molecular weight of 66kD and is tetrameric in low ionic strength buffers. The enzyme is not regulated by fructose 1,6-bisphosphate or by alanine and appears to resemble the M1 isoenzyme from rat liver most closely, although its activity is not inhibited by ATP.     

Purification and properties of pyruvate kinase from Thermoplasma acidophilum

Thermoplasma acidophilum is a thermoacidophilic archaebacterium occupying a paradoxical place in phylogenetic trees (phenotypically it is a thermoacidophile but phylogenetically it classifies with the methanogens). To better understand its phylogeny, the pyruvate kinase from this organism is being investigated as a molecular marker. The enzyme has been purified and has a native M(r) of 250,000. It consists of four, apparently identical subunits each of M(r) 60,000. No remarkable kinetic differences have been found between this thermophilic enzyme and its mesophilic counterparts other than its greater thermostability. Its amino acid composition has been determined and some partial sequencing has been done.     

Purification of four pyruvate kinase isozymes of rats by affinity elution chromatography.

1. Purification of four isozymes of pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) L, M1, M2 and R was much improved to give good yields by affinity elution chromatography. The enzyme was eluted from a phosphocellulose column with 0.5 mM phosphoenolpyruvate. Types L, M2 and R were stabilized with fructose 1,6-diphosphate throughout the purification procedures. 2. The isozymes were crystallized under various conditions: types L and R were readily crystallized from medium of low ionic strength, types L, M1, and M2 were crystallized from ammonium sulfate solution in different forms in the presence and absence of phosphoenolpyruvate. Type M1 was also crystallized in different forms in the presence and absence of fructose 1,6-diphosphate. 3. Amino acid analyses showed that the compositions of types L and R, and of types M1 and M2, respectively, were very similar.     

Purification and properties of pyruvate dehydrogenase kinase from bovine kidney

Pyruvate dehydrogenase kinase was purified about 2,700-fold to apparent homogeneity from extracts of bovine kidney mitochondria. The kinase consists of two subunits (alpha beta) with molecular weights of 48,000 (alpha) and 45,000 (beta) as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Kinase activity resides in the alpha subunit. The alpha subunit is sensitive to proteolysis by chymotrypsin, whereas the beta subunit is selectively modified by trypsin. These observations, together with the results of peptide mapping, indicate that the two subunits are distinctly different proteins. It is proposed that the beta subunit is a regulatory subunit.     

Evolution of the functional properties of pyruvate kinase isozymes: pyruvate kinase L fromRana pipiens

Summary The regulatory properties of type L pyruvate kinase fromRana pipiens are intermediate between those of the mammalian K and L isozymes. As with mammalian type L, the levels of the frog isozyme are affected by the animal's nutritional state. The mammalian and amphibian isozymes show similar sensitivities to fructose 1,6-bisphosphate activation and amino acid inhibition. By contrast, the frog L isozyme shares several properties of the K class: ie. irreversible inactivation by oxidized glutathione and lack of response to a cyclic AMP stimulated phosphorylation. Furthermore, as for some mammalian K isozymes, frog type L shows a high PEP affinity and a low cooperativity of PEP binding.Insofar as the properties of this present day enzyme reflect those of its counterpart in the amphibian ancestor of higher vertebrates, our results suggest that at its first expression, the type L resembled the type K. Many important regulatory properties of the L isozyme, especially the sensitivity to phosphorylation, were acquired more recently perhaps in association with an increased importance of constant blood glucose.Abbreviations DTT dithiothreitol - EDTA ethylenediamine tetraacetic acid - EGTA ethyleneglycol-bis(2-aminoethylether)-N,N-tetraacetic acid - FB fructose-1,6-bisphosphate - PEP phosphoenolpyruvate - PK pyruvate kinase     

Purification and molecular properties of the AMP-activated pyruvate kinase from Escherichia coli.

The AMP-activated pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from Escherichia coli has been purified 200 times through a three-step procedure which gives a homogeneous preparation with a specific activity of 110. The enzyme appears to be a tetramer of molecular weight 190 000. Subunits (molecular weight 51 000) show a single amino-terminal amino acid (serine) and appear as a single band in polyacrylamide gel electrophoresis in sodium dodecyl sulphate. The enzyme crystallizes in conditions of reduced dielectric constant of the solvent in the pH range 6.5-7.5. Kinetic and regulatory properties of the purified enzyme are similar to those described for crude preparations of the enzyme.     

Purification and characterization of two isozymes of 3-phosphoglycerate kinase from the mouse.

Two isozymes of 3-phosphoglycerate kinase (ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3), designated PGK-A and PGK-B, were purified from separate extracts of muscle and testicular tissue of DBA/2J mice, respectively. A similar procedure was used to purify the corresponding isozymes from C57BL/6J mice in order to make inter-strain comparisons. The purification involved the use of affinity chromatography with an 8-(6-aminohexyl)amino-ATP-Sepharose column and DEAE-Sephadex chromatography. Lactate dehydrogenase isozyme LDH-X was also co-purified from extract of mouse testes by this two-step procedure. The same isozyme isolated from either mouse strain was found to be identical in physical and biochemical properties. Both isozymes are monomeric as determined by gel filtration chromatography and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Furthermore, the isozymes have similar molecular weights, of 47 000 +/- 2000 and exhibit similar Km values for both coenzymes and substrate, as well as temperature dependence of enzyme activity. However, it was observed that the B isozyme is more labile than the A isozyme by denaturation at high temperature, urea and acidic pH.     

Purification and properties of pyruvate kinase from the hepatopancreas of Carcinus maenas.

Pyruvatekinase from the hepatopancreas of the common shore crab, Carcinus maenas, was purified to a specific activity of 240 units/mg of protein in the assay conditions described. 2. In one method of purification the enzymic activity could be resolved into two fractions after chromatography on DEAE-cellulose. Fructose 1, 6-diphosphate was able to effect the conversion of one form (peak 1) into the second (peak 2). 3. In the presence of a saturating concentration of fructose 1, 6-diphosphate both forms of the enzyme were kinetically similar. 4. Polyacrylamide-gel electrophoresis of the enzyme 1 day after preparation showed a single protein band. On storage at least three protein bands became visible, all of which were associated with pyruvate kinase activity. 5. Chromatography of the enzyme on Sephadex G-200 indicated a mol.wt. of 247000, but in the presence of fructose 1, 6-diphosphate the elution volume of the enzyme increased corresponding to a mol.wt. of 193000. 6 Dissociation of the enzyme in sodium dodecyl sulphate and 2-mercaptoethanol followed by polyacrylamide-gel electrophoresis produced one major protein band with a mol.wt. of 55000.     

Purification and properties of pig heart pyruvate kinase

Using essentially a two-step procedure involving phosphocellulose column chromatography followed by gel filtration on Sephadex G200, pig heart pyruvate kinase (PH PyK) was purified 267-fold to at least 97% purity. PH PyK co-sedimented with rabbit muscle PyK during sucrose density ultracentrifugation yielding an S_20,w of 10 and a corresponding molecular weight of about 237,000. Sodium docedyl sulfate polyacrylamide gel electrophoresis yielded a subunit molecular weight of approximately 59,000, suggesting that native PH PyK exists as a tetramer. The isoelectric point (pI) was determined to be 8.2, and thepH optimum (pHo) for the forward reaction is 7.2. Steady-state kinetics with phospho(enol)pyruvate (PEP) as the variable substrate show that there is a threefold decrease in the Km for PEP in the presence of 1.0 mM fructose-1,6-diphosphate (FDP), and that the activity of PH PyK is increased over fourfold by FDP at low (0.1 mM) PEP concentrations. Lineweaver-Burk plots are linear in the presence and absence of FDP, indicating that the Michaelis-Menten curves are hyperbolic. The amino acid composition for pig heart PyK shows close similarities between pig muscle and kidney PyKs, but not liver PyK. Among the data on pI,pHo, and FDP activation, only the activation by FDP is useful in tentatively designating pig heart PyK as an M₂ isozyme.Presented in partial fulfillment for the Master of Science degree.     

Purification and properties of rat brain pyruvate kinase

Rat brain pyruvate kinase was purified to near homogeneity by a three-step process involving ammonium sulfate precipitation and phosphocellulose and Blue-Sepharose CL-6B column chromatography. The enzyme migrated on polyacrylamide gel along with a commercial sample of rabbit muscle pyruvate kinase. The enzyme showed a hyperbolic relationship with phosphoenolpyruvate and ADP, with apparent Km's of 0.18 and 0.42 X 10(-3) M, respectively. The enzyme was inhibited by ATP, the effect being more pronounced at unsaturating concentrations of phosphoenolpyruvate. L-Phenylalanine was found to be a strong inhibitor of the enzyme, with the Ki for inhibitor being 0.11 mM. The inhibition by phenylalanine was more pronounced at pH 7.4 than at pH 7.0, and appeared to be competitive with phosphoenolpyruvate. L-Alanine and fructose 1,6-bisphosphate prevented the inhibition of the enzyme by phenylalanine. Ca2+ was found to be a strong inhibitor of the enzyme, and the inhibition was more marked at saturating phosphoenolpyruvate concentrations. The kinetic properties of the purified brain pyruvate kinase suggest that the enzyme may be distinct from the muscle or liver enzymes.