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At least 19 recordsLinked to original sources

PubMed1976

Magnetic circular dichroism of myoglobin-thiolate complexes.

Various complexes of myoglobin (Mb) with thiolate were studied by use of magnetic circular dichroism (MCD) spectroscopy. 1. MetMb-ethyl, n-propyl and isopropylmercaptan complexes offered MCD spectra similar to that of cytochrome P-450 (P-450) with respect to shape and intensity ratio of Soret MCD to Q0-0 MCD. The MCD spectra did not show any pH dependence. The complexes reduced by sodium dithionite exhibited the MCD spectrum of deoxyMb, indicative of release of thiolate anion from the heme iron. 2. Cysteine and cysteine methyl ester coordinated to the heme iron at pH 9.18 but not at pH 6.86 and 11.45. The complex formed at pH 9.18 gave an MCD spectrum similar to that of P-450, and an MCD spectrum of deoxy Mb on reduction with sodium dithionite. 3. The 2-mercaptoethanol complex exhibited three A terms associated with the Q0-0-1, and Soret transitions at pH 6.86 similar to those of Fe(II) cytochrome c, which indicates that Mb was reduced by this reagent at pH 6.86. At pH 9.18 2-mercaptoethanol gave an MCD spectrum similar to that of alkyl mercaptan just after the addition. With the time changed into deoxy Mb through some intermediate of reduced Mb-thiolate complex. At pH 11.45 2-mercaptoethanol formed complex which exhibited an MCD spectrum similar to those of other alkylmercaptans. 4. Sodium sulfide gave an MCD spectrum which resembled that of the normal thiol Mb complex just after addition at pH 6.86. The complex was gradually reduced to give 610 nm trough in addition to the MCD of deoxy Mb. The Mb-sulfur complex formed at pH 9.18 was gradually reduced to give an MCD spectrum which was fairly different from that of deoxy Mb. A similar MCD spectrum was observed at pH 11.45 just after the addition of Na2S. These results were considered to suggest the saturation of one of the conjugated double bonds of the porphyrin by sulfur.

Animals↗

PubMed1976

Reinvestigation of the phenacyl bromide modification of alpha-chymotrypsin.

The modification of alpha-chymotrysin with phenacyl bromide has been reinvestigated over a wide pH range. Evidence is presented that indicates that the nature of the phenacyl-modified enzymes prepared by this reaction is dependent upon the pH of the reaction medium. The phenacyl alpha-chymotrypsin produced at low pH is most probably the Met-192 phenacylsulfonium salt, as proposed earlier, since it readily undergoes dealkylation using 2-mercaptoethanol. However, the phenacyl-enzyme prepared at neutral pH possesses a much reduced enzymatic activity and does not react with 2-mercaptoethanol to regenerate native alpha-chymotrypsin. In addition, incubation of the Met-192 phenacyl sulfonium enzyme at neutral pH causes a smooth irreversible change to the new phenacyl-enzyme as monitored by changes in enzymatic activity, susceptibility to dealkylation using 2-mercaptoethanol, and ultraviolet difference absorption spectral properties. The stoichiometries of both the low and neutral pH modification reactions have been determined, using [carbonyl-14C]phyenacyl bromide, to be 1 phenacyl group/enzyme molecule. In efforts to obtain information about the nature and mechanism of formation of the phenacyl alpha-chymotrypsin produced at neutral pH, alkylation reactions of modified alpha-chymotrypsins produced by His-57 functionalization with tosylphenylalanine chloromethyl ketone and by Met-192 oxidation to the sulfoxide have been investigated. The combined results of these studies have been initially interpreted in terms of a neutral pH, phenacyl bromide modification resulting in formation of a new modified enzyme via the Met-192 sulfonium salt.

Acetophenones↗

PubMed1976

Novikoff hepatoma deoxyribonucleic acid polymerase. Sensitivity of the beta-polymerase to sulfhydryl blocking agents.

Unlike other beta-class eukaryotic DNA polymerases, the enzyme purified from the Novikoff hepatoma is inhibited by both sulfhydryl blocking agents N-ethylmaleimide (NEM) and p-hydroxymercuribenzoate (pHMB). The degree of sensitivity varies depending on the enzyme purity, pH of the reaction, and the presence of sulfhydryl reducing agents. Novikoff beta-polymerase activity is unaffected by the presence of 2-mercaptoethanol (2-Me) or dithiothreitol (DTT); however, the combination of 2-mercaptoethanol and NEM or pHMB acts to reverse the inhibition of the sulfhydryl blocking agent. The reversal of inhibition involves more than just a titration of NEM with 2-mercaptoethanol since a) the combination of these two reagents actually stimulates the DNA polymerase, and b) dithiothreitol did not reverse the inhibition. Binding of the polymerase to DNA did not affect the enzyme sensitivity to NEM.

Animals↗

PubMed1975

Amylase of the thermophilic actinomycete Thermomonospora vulgaris.

alpha-Amylase of the thermophilic actinomycete Thermomonospora vulgaris was partially purified. Maximal enzyme activity was obtained at 60degreeC and pH 6.0. KM value was l.4%. The effect of some metal salts on enzyme activity was studied. Enzyme activity was inhibited by by KCN, EDTA, and iodoacetate. Inhibition by EDTA was completely nullified by CaCl2, but the inhibition by iodoacetate was not overcome by 2-mercaptoethanol. Exposure of the enzyme to pH 7.0 and 9.0 for 2 hr. did not affect the enzyme, but exposure to pH 3.0 for few minutes completely inactivated the enzyme. Exposure of the enzyme to 60degreeC resulted in an appreciable inactivation and exposure to 80degreeC completely inactivated the enzyme. Addition of CaCl2, 2-mercaptoethanol, or enzyme substrate the 60degreeC exposed enzyme. However, bovine serym albumin had a protective effect when the enzyme was exposed to 60degreeC but not to 80degreeC. The enzyme was stable in the presence of 8 M urea.

Amylases↗

PubMed1975

Mercury inhibition of avian fatty acid synthetase complex.

(1) Subcutaneous or intra-abdominal injections of 8 mg of HgCl2/100 g body weight markedly depressed hepatic fatty acid synthetase activity of chicks at 1 h post-injection. The depression occurred despite the fact that the chicks continued to eat up until the time they were killed. Under these same conditions, the hepatic activity of acetyl-CoA carboxylase (EC 6.4.1.2) was not affected by HgCl2, while the activity of the mitochondrial system of fatty acid elongation was stimulated. (2) When 2-mercaptoethanol was included in the incubation medium for a highly purified preparation of fatty acid synthetase, 500 muM HgCl2 was required to show definite inhibition of the enzyme. When 2-mercaptoethanol was omitted, 50 muM HgCl2 was inhibitory and 100 muM HgCl2 abolished enzyme activity. (3) 2 mM dithiothreitol completely protected the purified fatty acid synthetase preparation from inhibition by 100 muM HgCl2. When dithiothreitol was added after the addition of enzyme to the mercury-containing medium, protection of the enzyme was not complete. (4) Dialysis of cytosol fractions from chicks injected with HgCl2 against 500 vol. of 0.2 M potassium phosphate buffer (pH 7.0) containing 1 mM EDTA and 10 mM dithiothreitol for 4 h at 4 degrees stimulated the fatty acid synthetase activity of the fractions. Dialysis of cytosol fractions from noninjected chicks under the same conditions was without effect on fatty acid synthetase activity. (5) These data support the hypothesis that the inhibitory effect of HgCl2 administered in vivo on hepatic fatty acid synthetase activity in chicks is mediated through the interaction of mercury with the sulfhydryl groups of the enzyme.

Acetyl-CoA Carboxylase↗

PubMed1976

Isolation and properties of alpha-D-mannosidase from human kidney.

Alpha-D-Mannosidase activity exists in three forms that can be separated by DEAE-cellulose chromatography, alpha-D-Mannosidase was isolated from human kidney in a homogeneous state, and was purified 2100-fold, with p-nitrophenyl alpha-D-mannoside as substrate. The purified alpha-D-mannosidase was practically free from all other glycosidases tested. The Km of the synthetic substrate with the enzyme was 1 X 10(-3) M and the pH optimum 4.5. It was inhibited by heavy metals, sodium dodecyl sulphate, urea and compounds that react with the thiol groups, and was activated by Zn2+, Na+, 2-mercaptoethanol, human albumin and gamma-globulin. The mol. wt. of the enzyme was estimated to be 180 000 +/- 4500. After pretreatment with 2-mercaptoethanol and sodium dodecyl sulphate, alpha-D-mannosidase dissociated into subunits of mol. wts. of 58 000 +/- 600 and 30 000 +/- 380 respectively. Subunits of the same molecular weights were also obtained after the enzyme was heated at 100 degrees C.

Ammonium Sulfate↗

PubMed1976

Monomeric purine nucleoside phosphorylase from rabbit liver. Purification and characterization.

Rabbit liver purine nucleoside phosphorylase (purine nucleoside: orthophosphate ribosyltransferase EC 2.4.2.1.) was purified to homogeneity by column chromatography and ammonium sulfate fractionation. Homogeneity was established by disc gel electrophoresis in presence and absence of sodium dodecyl sulfate, and isoelectric focusing. Molecular weights of 46,000 and 39,000 were determined, respectively, by gel filtration and by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Product inhibition was observed with guanine and hypoxanthine as strong competitive inhibitors for the enzymatic phosphorolysis of guanosine. Respective Kis calculated were 1.25 x 10(-5) M for guanine and 2.5 x 10(-5) M for hypoxanthine. Ribose 1-phosphate, another product of the reaction, gave noncompetitive inhibition with guanosine as variable substrate, and an inhibition constant of 3.61 x 10(-4) M was calculated. The protection of essential --SH groups on the enzyme, by 2-mercaptoethanol or dithiothreitol, was necessary for the maintenance of enzyme activity. Noncompetitive inhibition was observed for p-chloromercuribenzoate with an inhibition constant of 5.68 x 10(-6)M. Complete reversal of this inhibition by an excess of 2-mercaptoethanol or dithiothreitol was demonstrated. In the presence of methylene blue, the enzyme showed a high sensitivity to photooxidation and a dependence of photoinactivation on pH, strongly implicating histidine as the susceptible group at the active site of the enzyme. The pKa values determined for ionizable groups of the active site of the enzyme were near pH 5.5 and pH 8.5 The chemical and kinetic evidences suggest that histidine and cysteine may be essential for catalysis. Inorganic orthophosphate (Km 1.54 x 10(-2) M) was an obligatory anion requirement, and arsenate substituted for phosphate with comparable results. Guanosine (Km 5.00 x 10(-5) M), deoxyguanosine (Km 1.00 x 10(-4)M) and inosine (Km 1.33 x 10(-4)M), were substrates for enzymatic phosphorolysis. Xanthosine was an extremely poor substrate, and adenosine was not phosphorylyzed at 20-fold excess of the homogeneous enzyme. Guanine (Km 1.82 x 10(-5)M),ribose 1-phosphate (Km 1.34 x 10(-4) M) and hypoxanthine were substrates for the reverse reaction, namely, the enzymatic synthesis of nucleosides. The initial velocity studies of the saturation of the enzyme with guanosine, at various fixed concentrations of inorganic orthophosphate, suggest a sequential bireactant catalytic mechanism for the enzyme.

Animals↗

PubMed2026

2-Mercaptoethanol/DMSO Workflow Enables Highly Reproducible Quantitative Proteomics.

Proteomics provides a systematic and high-throughput approach to comprehensively characterize protein networks, enabling insights into cellular functions and disease mechanisms. Carbamidomethylation using iodoacetamide (IAA), a common method for cysteine alkylation, is known to cause nonspecific modifications that increase spectral complexity in mass spectrometry and reduce quantitative accuracy. Here, we established a reproducibility-focused 2-mercaptoethanol (2-ME)/dimethyl sulfoxide (DMSO) workflow and systematically evaluated its quantitative performance at the proteome-wide level. Mouse liver proteomes were processed using either 2-ME/DMSO or conventional IAA treatment, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The optimized 2-ME treatment increased the number of cysteine-modified peptides by 1.6- to 1.9-fold. Although total protein identifications were comparable, 77% of proteins exhibited improved sequence coverage with the optimized 2-ME treatment. Quantitative reproducibility was also enhanced, with the peptide quantified CV ≤ 20% increasing from 61.4% with IAA treatment to 86.1% with 2-ME treatment, and protein quantified CV ≤ 20% increasing from 80.6% with IAA treatment to 93.5% with 2-ME treatment. Application of this new workflow to ovarian clear cell carcinoma reliably detected cisplatin-induced alterations. The 2-ME/DMSO workflow offers a simple and highly reproducible proteomics strategy for accurate quantitative proteomics.

Animals↗

PubMed1975

The effect of disulfiram on the aldehyde dehydrogenases of sheep liver.

1. The effect of disulfiram on the activity of the cytoplasmic and mitochondrial aldehyde dehydrogenases of sheep liver was studied. 2. Disulfiram causes an immediate inhibition of the enzyme reaction. The effect on the cytoplasmic enzyme is much greater than on the mitochondrial enzyme. 3. In both cases, the initial partial inhibition is followed by a gradual irreversible loss of activity. 4. The pH-rate profile of the inactivation of the mitochondrial enzyme by disulfiram and the pH-dependence of the maximum velocity of the enzyme-catalysed reaction are both consistent with the involvement of a thiol group. 5. Excess of 2-mercaptoethanol or GSH abolishes the effect of disulfiram. However, equimolar amounts of either of these reagents and disulfiram cause an effect greater than does disulfiram alone. It was shown that the mixed disulphide, Et2N-CS-SS-CH2-CH2OH, strongly inhibits aldehyde dehydrogenase. 6. The inhibitory effect of diethyldithiocarbamate in vitro is due mainly to contamination by disulfiram.

Aldehyde Oxidoreductases↗

PubMed1976

A clottable protein (coagulogen) from amoebocyte lysate of Japanese horseshoe crab (Tachypleus tridentatus). Its isolation and biochemical properties.

A clottable protein, named coagulogen, was highly purified from the amoebocyte lysate of Japanese horseshoe crab (Tachypleus tridentatus) by a method similar to that used for the lysate of Limulus polyphemus amoebocytes. The isolated material gave a single protein band on analytical gel electrophoresis at pH 3.2, gel electrofocusing, and sodium dodecyl sulfate (SDS) gel electrophoresis with or without 2-mercaptoethanol. It was 90 percent coagulable, and the total yield from 10 ml of the amoebocyte lysate was about 40 mg. The sedimentation coefficient of purified coagulogen was 2.6 S and its molecular weight was estimated to be about 15,300 by sedimentation equilibrium analysis. The molecular weight estimated by SDS-gel electrophoretic analysis was 19,500 +/- 1,000. This discrepancy was apparently due to abnormal mobility arising from the basic nature of this protein on electrophoresis. The protein had a high isoelectric point of pH 10.0 +/- 0.2, as measured by the isoelectric focusing technique. It consisted of a total of 132 to 135 amino acid residues and contained high levels of basic amino acids, which accounted for more than 16 per cent of the total amino acid residues. No methionine was detected. High contents of valine, half-cystine, glutamic acid (glutamine), and phenylalanine were found. The N-terminal sequence of the first three residues of the coagulogen was Ala-Asx-Thr, and its C-terminal residues was identified as phenylalanine, indicating that it consists of a single polypeptide chain. It is of interest that the first three N-terminal residues are homologous with those of the Aalpha-chain of non-human primate fibrinogen.

Amino Acids↗

PubMed1976

Properties of Fcgamma receptors in normal and malignant human tissues.

Properties of the IgG receptors were studied by treating tissue sections or suspensions of peripheral mononuclear cells with various chemical reagents and determining changes in their ability to react with IgG-sensitized erythrocytes (EA). A heterogeneity of the Fc receptors was revealed. Iodoacetamide, 2-mercaptoethanol, sodium azide, EDTA, and a pH varying from 6.0 to 8.2 had no effect on Fc receptors in sections of normal lymphoreticular tissue and malignant tissue. Formaldehyde, low pH, and high salt concentrations affected receptor activity to various degrees. Receptors in liver sections and on monocytes were generally more resistant than receptors in spleen sections and on B lymphocytes. Receptors in malignant tissue behaved either like receptors in spleen or like receptors in liver. Although all tissues were sensitive to periodic acid, the Fc receptors in malignant tissue were always more resistant.

Azides↗

PubMed1975

Hydroxylation of p-Coumaric acid by illuminated chloroplasts. The role of superoxide.

1. Chloroplasts isolated from leaves of spinach-beet (Beta vulgaris L. ssp. vulgaris) do not catalyse the hydroxylation of p-coumaric acid in the dark unless a reductant (such as ascorbate, NADH or NADPH) is added. Superoxide dismutase has no effect on this reaction. 2. Illuminated chloroplasts catalyse the hydroxylation in the absence of added reductant. This reaction is completely inhibited by superoxide dismutase, but catalase has little effect. 3. Both hydroxylation in the light and hydroxylation in the dark in the presence of reductants are inhibited by diethyldithiocarbamate, EDTA, cyanide and 2-mercaptoethanol. 4. It is proposed that O-2- generated by illuminated chloroplasts is involved in the provision of a reductant to the enzyme phenolase.

Ascorbic Acid↗

PubMed1976

Fluroescence of proteins in 6-M guanidine hydrochloride. A method for the quantitative determination of tryptophan.

To determine the tryptophan content in proteins,an analytical ultraviolet fluroescence method is proposed based on making uniform the environment of aromatic chromophores in 6-7 M guanidine hydrochloride. The fluorescence intensity scale is calibrated using standard solutions of free tryptophan. A correlation coefficient between the fluorescence of protein tryptophanyl residues and of free tryptophan was estimated in testing 17 well characterized proteins. This method is particularly suited to proteins carrying groups absorbing in the 290-370 nm region, such as flavin, heme and pyridoxal phosphate and in the presence of substances such as 2-mercaptoethanol which prohibit the use of the spectroscopic or magnetic circular dichroism methods. It is less time-consuming than techniques requiring hydrolysis or chemical reactions.

Guanidines↗

PubMed1976

Membrane-bound DD-carboxypeptidase and transpeptidase activities from Bacillus megaterium KM at pH 7. General properties, substrate specificity and inhibition by beta-lactam antibiotics.

1. The membranes from Bacillus megaterium KM contained a DD-carboxypeptidase with optimum activity under the following conditions: pH 7; ionic strength, 1.3 M; temperature, 40 degrees C and below 20 degrees C. It did not require any divalent cation, but was inactivated by Cu2+ and Hg2+. It was stimulated by 2-mercaptoethanol and low concentrations of p-chloromercuribenzoate. 2. The membrane preparation also catalyzed a simple transpeptidation reaction using as carboxyl acceptors D-alanine or glycine. 3. The conditions for optimum activity, temperature-inactivation, temperature-dependence of the activity, carboxyl donor specificity, sensitivity to beta-lactam antibiotics, and insensitivity to potential peptide inhibitors of both enzyme activities, was identical. The DD-carboxypeptidase showed inhibition by D-alanine and Ac2-L-Lys-D-Ala. 4. The inhibition by beta-lactam antibiotic was reversible for both enzymic activities and the time-dependence for their recovery was identical. 5. The DD-carboxypeptidase was very sensitive to changes in the configuration and size of the side-chains of the C-terminal dipeptide of the substrate. Amino acid residues at the C-terminus that precluded the peptide from being a DD-carboxypeptidase substrate were not acceptors in the transpeptidation reaction. Dipeptides were not acceptors for the 'model transpeptidase'. 6. It is suggested that both activities are catalysed by the same enzyme molecule, whose physiological role is not the formation of peptide crosslinks during peptidoglycan biosynthesis.

Acyltransferases↗

PubMed1976

Purification and characterization of N-hydroxy-2-acetylaminofluorene sulfotransferase from rat liver.

N-Hydroxy-2-acetylaminofluorene (N-OH-2-AAF) sulfotransferase is an enzyme that catalyzes the sulfate transfer from the active sulfate, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), to N-OH-2-AAF to form a highly reactive product acetylaminofluorene N-sulfate. It has been purified about 2000-fold with a yield of over 12% from adult Sprague-Dawley male rat livers by an eight-step procedure. The final preparation was homogeneous on analytrical disc gel electrophoresis. The purified enzyme had activity toward p-nitrophenol with an approximately 1600-fold increase in specific activity over the crude homogenate, but it had almost no detectable activity toward steroids such as estrone, beta-estradiol, testosterone, dehydroisoandrosterone, and corticosterone. There was also very little sulfation activity toward serotonin and L-tyrosine methyl ester. The optimal pH for the enzyme activity is approximately 6.3 when measured in sodium phosphate buffer. Mg2+ at 6 to 9 mM could increase the enzyme activity up to 30%. Mn2+ activated the enzyme only slightly at very low concentrations. Zn2+, Co2+, Cu2+, and Ni2+ were all strongly inhibitory, but Ca2+ had very little effect. Thiol compounds were found to have a stabilizing effect and thiol-blocking reagents were potent inhibitors for this enzyme. The pure enzyme was very unstable especially in diluet solutions. The isoelectric point (pl) of the enzyme is 5.66 +/- 0.07. The molecular weight of the native enzyme was 68,000 +/- 500 as estimated by Sephadex G-100 and G-200 gel filtrations. A single component with molecular weight of 38,250 +/- 1,350 was observed on sodium dodecyl sulfate gel electrophoresis in the absence and presence of 2-mercaptoethanol. Comparison of the enzyme activity in mail and female rat livers at each stage of purification revealed that there was only a trace amount of N-OH-2-AAF sulfotransferase present in the female rat liver.

Animals↗

PubMed1976

A new oxygenase, 2-nitropropane dioxygenase of Hansenula mrakii. Enzymologic and spectrophotometric properties.

2-Nitropropane dioxygenase, purified to homogeneity from Hansenula mrakii (IFO 0895), has a molecular weight of approximately 62,000 and consists of two subunits nonidentical in molecular weight (39,000 and 25,000). Stoichiometrical studies and the results obtained with 18O2 showed that 2 atoms of molecular oxygen are incorporated into 2 molecules of acetone formed from 2-nitropropane. In addition to 2-nitropropane, nitroethane, 3-nitro-2-pentanol, and 1-nitropropane are oxidatively dentrified. The enzyme, which exhibits absorption maxima at 274, 370, 415, and 440 nm and a shoulder at 470 nm, contains 1 mol of FAD and 1 g atom of non-heme iron per mol of enzyme. The enzyme-bound FAD is reduced by 2-nitropropane under anaerogic conditions, but the enzyme-bound Fe3+ is not affected. The introduction of oxygen to the reduced form of enzyme causes reoxidation of the enzyme. The bound FAD and Fe3+ are reduced by the addition of nitromethane, which is not a substrate, under anaerobic conditions. The aerobic dialysis of the enzyme treated with nitromethane causes reoxidation of only the Fe2+. Sodium dithionite also reduces both the enzyme-bound FAD and Fe3+ under anaerobic conditions. When the enzyme is dialyzed against 10 mM potassium phosphate buffer (pH 7.0) immediately after reduction by dithionite, the absorption spectrum similar to that of the native enzyme appeared with concomitant restoration of approximately 80% of the activity. The enzyme activity is significantly inhibited by pyrocatechol-3,5-disulfonate disodium salt, 8-hydroxyquinoline, reducing agents such as 2-mercaptoethanol, and HgCl2. The Michaelis constants are as follows: 2-nitropropane (2.13 X 10(-2) M), nitroethane (2.43 X 10(-2) M), 3-nitro-2-pentanol (6.8 X 10(-3) M), 1-nitropropane (2.56 X 10(-2) M), and oxygen (3.03 X 10(-4) M, with 2-nitropropane).

Amino Acids↗

PubMed1976

Identification of albumin as the serum factor essential for the growth of activated human lymphocytes.

Albumin from human, bovine, or rabbit serum supported the growth of concanavalin A-stimulated human thymus-derived lymphocytes equally well. This activity was completely abolished by pepsin digestion. It was shown for bovine serum albumin that the albumin molecule itself, and neither an impurity nor a factor bound to albumin was essential for the growth of lymphocytes. This conclusion was based on observations that the growth-promoting activity could not be removed from albumin, and that the specific activity of albumin remained unaltered after the following procedures: molecular sieving at pH 7.5 at pH 3.0, and in 8 M urea at pH 6.6; ion exchange chromatography at pH 4.3 and in 8 M urea at pH 7.2; isoelectric focusing; charcoal treatment; acetone precipitation; and reduction with 2-mercaptoethanol in the presence of 8 M urea. Dimeric albumin was found to support growth of lymphocytes as well as monomeric albumin, and mercaptalbumin and non-mercaptalbumin were shown to have equal activity.

Animals↗

PubMed1975

Decarboxylation of oxalacetate to pyruvate by purified avian liver phosphoenolpyruvate carboxykinase.

Phosphoenolpyruvate carboxykinase, which has been isolated from chicken liver mitochondria in essentially homogenous form, carries out the irreversible decarboxylation of oxalacetate to pyruvate in the presence of catalytic amounts of GDP or IDP, as well as the reversible decarboxylation of oxalacetate to phosphoenolpyruvate in the presence of substrate amounts of GTP or ITP. The pyruvate- and phosphoenolpyruvate-forming reactions are similar in their nucleoside specificity and appear to be carried out by the same protein. However, the two activities vary markedly in their response to added metal ions and sulfhydryl reagents. Phosphoenolpyruvate formation is completely dependent on the presence of a divalent metal ion, with Mn2+ the most effective species. This reaction is also stimulated by sulfhydryl reagents such as 2-mercaptoethanol. In contrast, the pyruvate-forming reaction is strongly inhibited by divalent metal ions, including Mn2+, and also by moderate concentrations of sulfhydryl reagents. These observations and the demonstration that pyruvate kinase-like activity is very low or absent make it unlikely that pyruvate formation proceeds via phosphoenolpyruvate as an intermediate. Although the pyruvate-forming reaction is inhibited by added metal ions, the reaction is also inhibited by metal-chelating agents such as 8-hydroxyquinoline and o-phenanthroline, suggesting that the reaction is dependent on the presence of a metal ion. It has not been possible, however, to demonstrate that the enzyme is a metalloprotein.

2,2'-Dipyridyl↗