Purification and partial characterization of adenosine diphosphatase activity in bovine aorta microsomes

Anti-aggregatory activities in bovine aorta microsomal fractions were solubilized with Triton X-100 and separated into two fractions by DEAE-Sepharose CL-6B. One fraction strongly inhibited arachidonic acid-induced platelet aggregation, and the other inhibited ADP-induced aggregation. The latter fraction contained ADPase activity. The ADPase activity was further purified by affinity chromatography. The purified enzyme had specific activities of 43.8 and 48.2 mumol of Pi/min/mg protein for ADP and ATP, respectively. The enzyme required calcium or magnesium ions and it was insensitive to ATPase inhibitors, namely oligomycin and ouabain, and to adenylate kinase inhibitor, Ap5A. Polyacrylamide gel electrophoretic experiments indicated that only one enzyme was involved. This was confirmed by the parallel behavior of ADPase and ATPase activities throughout all the purification steps. These results suggest that the main anti-aggregatory activity of bovine aorta microsomes for ADP-induced aggregation is due to an ATP diphosphohydrolase (EC 3.6.1.5).

Pathway for inositol 1,3,4-trisphosphate and 1,4-bisphosphate metabolism

We prepared [3H]inositol-,3-[32P]phosphate-and 4-[32P]phosphate-labeled inositol phosphate substrates to investigate the metabolism of inositol 1,3,4-trisphosphate and inositol 1,4-bisphosphate. In crude extracts of calf brain, inositol 1,3,4-trisphosphate is first converted to inositol 3,4-bisphosphate, then the inositol 3,4-bisphosphate intermediate is further converted to inositol 3-phosphate. Similarly, inositol 1,4-bisphosphate is converted to inositol 4-phosphate, and no inositol 1-phosphate is formed. We partially purified an enzyme that we tentatively name inositol polyphosphate 1-phosphatase. This cytosolic enzyme converts inositol 1,3,4-trisphosphate to inositol 3,4-bisphosphate and also converts inositol 1,4-bisphosphate to inositol 4-phosphate. The enzyme does not utilize inositol 1,3,4,5-tetrakisphosphate, inositol 1,4,5-trisphosphate, or inositol 1-phosphate as substrates. Thus we propose a new scheme for inositol phosphate metabolism. According to this pathway inositol 1,4,5-trisphosphate and inositol 1,4-bisphosphate are degraded to inositol 4-phosphate. Inositol 1-phosphate, which is the major inositol monophosphate formed in stimulated brain, is derived either from phospholipase C cleavage of phosphatidylinositol or from the degradation of inositol cyclic phosphates.

Specific magnesium-dependent diadenosine 5',5'''-P1,P3-triphosphate pyrophosphohydrolase in Escherichia coli

A specific Mg2+-dependent bis(5'-adenosyl)-triphosphatase (EC 3.6.1.29) was purified 270-fold from Escherichia coli. The enzyme had a strict requirement for Mg2+. Other divalent cations, such as Mn2+, Ca2+, or Co2+, were not effective. The products of the reaction with bis(5'-adenosyl) triphosphate (Ap3A) as the substrate were ADP and AMP in stoichiometric amounts. The Km for Ap3A was 12 +/- 5 microM. Bis(5'-adenosyl) di-, tetra-, and pentaphosphates, NAD+, ATP, ADP, AMP, glucose 6-phosphate, p-nitrophenylphosphate, bis-p-nitrophenylphospate, and deoxyribosylthymine-5'-(4-nitrophenylphosphate) were not substrates of the reaction. The enzyme had a molecular mass of 36 kilodaltons (as determined both by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis), an isoelectric point of 4.84 +/- 0.05, and a pH optimum of 8.2 to 8.5. Zn2+, a known potent inhibitor of rat liver bis(5'-adenosyl)-triphosphatase and bis(5'-guanosyl)-tetraphosphatase (EC 3.6 1.17), was without effect. The enzyme differs from the E. coli diadenosine 5',5'''-P1, P4-tetraphosphate pyrophosphohydrolase which, in the presence of Mn2+, also hydrolyzes Ap3A.

Binding of zinc(II) to beta-D-fructose 2,6-bisphosphate

The formation of a complex between Zn(II) and beta-D-fructose 2,6-bisphosphate was shown because the latter compound: activated bis(5'-guanosyl)tetraphosphatase (EC 3.6.1.17) and dinucleoside triphosphatase (EC 3.6.1.29) only to the extent that they could be inhibited by Zn(II); increased the consumption of Zn(II) necessary to titrate to an end point a solution of the metallochromic indicator eriochrome black T; coeluted with Zn(II) in a gel filtration column capable of resolving them if unbound. Neither of those effects was shown by D-fructose 1,6-bisphosphate under the same conditions.

Enzymic dephosphorylation of D-myo-inositol 1,4-bisphosphate in rat brain

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and inositol 1,4-bisphosphate [Ins(1,4)P2] phosphatase activities were measured in both 180,000 g (60 min) particulate and supernatant fractions of rat brain homogenates. Although Ins(1,4,5)P3 was mostly hydrolysed by a particulate phosphatase [Erneux, Delvaux, Moreau & Dumont (1986) Biochem. Biophys. Res. Commun. 134, 351-358], Ins(1,4)P2 phosphatase was predominantly soluble. The latter enzyme was Mg2+-dependent and sensitive to thiol-blocking agents (e.g. p-hydroxymercuribenzoate). In contrast with Ins(1,4,5)P3 phosphatase activity measured in the soluble fraction, Ins(1,4)P2 phosphatase was insensitive to 0.001-1 mM-2,3-bisphosphoglycerate. Lithium salts, widely used in psychiatric treatment, inhibited both Ins(1,4)P2 and Ins(1)P1 phosphatase activities of the crude soluble fraction. In particular, 50% inhibition of phosphatase activity, with 2 microM-Ins(1,4)P2 as substrate, was achieved at 3-5 mM-LiCl. At these concentrations, LiCl did not change Ins(1,4,5)P3 phosphatase activity measured in the same fraction with 1-4 microM-Ins(1,4,5)P3 as substrate. Chromatography of the soluble fraction of a rat brain homogenate on DEAE-cellulose resolved three phosphatase activities. These forms, peaks I, II and III, dephosphorylated Ins(1,4,5)P3, Ins(1)P1 and Ins(1,4)P2 respectively. If LiCl (10 mM) was included in the assay mixture, it inhibited both peak-II Ins(1)P1 phosphatase and peak-III Ins(1,4)P2 phosphatase, suggesting the existence of at least two Li+-sensitive phosphatases.

Messenger RNA guanylyltransferase from Saccharomyces cerevisiae. Large scale purification, subunit functions, and subcellular localization

Messenger RNA capping enzyme (GTP:mRNA guanylyltransferase) purified from yeast Saccharomyces cerevisiae consisted of two polypeptides (45 and 39 kDa) and possessed two enzymatic activities, i.e. mRNA guanylyltransferase and RNA 5'-triphosphatase (Itoh, N., Mizumoto, K., and Kaziro, Y. (1984) J. Biol. Chem. 259, 13923-13929). In this paper, we describe an improved procedure suitable for the large scale purification of the enzyme. The steps include glass beads disruption of the cells and several ion-exchange and affinity column chromatographies. The enzyme was purified from kilogram quantities of yeast cells to apparent homogeneity. The purified enzyme had an approximate Mr of 180,000 and consisted of two heterosubunits of 80 and 52 kDa and had the same two enzymatic activities as above. We consider that this is the more intact form of the enzyme. Using the in situ assays on sodium dodecyl sulfate-polyacrylamide gels, RNA 5'-triphosphatase, and mRNA guanylyltransferase activities were located on the 80- and 52-kDa chains, respectively. In agreement with this, the 52-kDa enzyme-[32P]GMP complex was formed on incubation of the enzyme with [alpha-32P]GTP. Guinea pig antisera against purified yeast capping enzyme recognized both 80- and 52-kDa chains in Western blot analysis. The antibody did not cross-react with the enzymes from rat liver. Artemia salina, or vaccinia virus. Nuclear localization of the enzyme was demonstrated by immunofluorescence microscopy.

Partial purification and characterization of an aldohexose 1-P phosphatase from pig skeletal muscle

An enzyme with a molecular weight of 54,000 which possesses phosphatase activity acting on glucose 1-P, galactose 1-P and mannose 1-P has been partially purified and characterized from pig skeletal muscle. The enzyme is free of phosphoglucomutase and galactokinase activities, and it possesses a neutral optimum pH. Pi acts as an inhibitor; glucose, galactose and mannose do not produce any effect. Divalent cations are required for activity, Mg2+ being the most effective activator. Micromolar levels of fluoride and millimolar levels of chloride act as inhibitors; however, vanadate does not produce any effect. The enzyme may have an important role when galactose accumulates in tissues; for example, in galactosemic patients and in young animals ingesting high-galactose diets.

Nucleoside-triphosphatase and hydrolysis of thiamin triphosphate in Escherichia coli

A membrane-bound nonspecific triphosphatase of E. coli was solubilized and purified to a homogeneous SDS-acrylamide gel electrophoresis band. It was found to be a single polypeptide of 16 kDa requiring no Mg2+, with an optimal pH at 6.5. The substrate specificity was broad and a nonspecific Mg2+-independent ribonucleoside-triphosphatase (NTPase) activity was expressed together with thiamin-triphosphatase activity. The molecular size and characteristics were clearly different from the known NTPase (EC 3.6.1.15). Using the purified thiamin-triphosphatase II, ATP:thiamin-diphosphate phosphoryl transferase (EC 2.7.4.15) activity was demonstrated with an optimal pH of approx. 5.3. Considering its kinetic parameters and other characteristics, however, the thiamin triphosphate synthesizing activity was not thought to take part in cellular thiamin triphosphate synthesis. The possibility that thiamin-triphosphatase II plays a part in the hydrolysis of thiamin triphosphate to control its cellular level is suggested.

The mechanism of activation of heart fructose 6-phosphate,2-kinase:fructose-2,6-bisphosphatase

Partially purified fructose-6-P,2-kinase:fructose-2,6-bisphosphatase from beef heart was phosphorylated by cAMP protein kinase. The phosphorylated fructose-6-P,2-kinase shows lower Km for Fru-6-P (43 versus 105 microM) and for ATP (0.55 versus 1.3 mM) but no change in the Vmax, compared to those for unphosphorylated enzyme. There was no detectable change in Km or Vmax of fructose-2,6-bisphosphatase activity by the phosphorylation. These changes in heart fructose-6-P,2-kinase were in direct contrast to previous results for the liver isozyme in which phosphorylation led to inhibition of the kinase activity and activation of the phosphatase activity.

Identification and characterization of a specific dolichylmonophosphate phosphatase activity in bovine thyroid microsomes

Bovine thyroid membranes are able to dephosphorylate exogenous [1-3H]DMP as well as endogenous prelabeled [32P]DMP. The kinetics, properties and specificity of the dolichylmonophosphatase activity have been studied by monitoring respectively the release of [1-3H]dolichol from [1-3H]DMP and the residual amount of [32P]DMP. The DMP-phosphatase activity is not linear with respect to time and exhibits a neutral pH optimum. There is only linearity in a narrow range of protein concentration when 0.25% Triton X-100 is included in the incubation mixture. Studying the enzymatic activity in function of protein concentration, the detergent requirement shows to be very critical. Triton X-100 is necessary for enzymatic activity with [1-3H]DMP (only 10% of enzymatic activity in the absence of detergent) although the detergent inhibits the hydrolysis of endogenous prelabeled [32P]DMP. Divalent cations are not essential for enzymatic activity, Ca2+-ions being even inhibitory. In accordance, EDTA (EGTA) is slightly stimulatory. The DMP-Pase activity is not influenced by the ionic strength of the incubation system and sulphydryl groups are not involved. NaF, VOS and VO4(3-) are strongly inhibitory. The inhibition by dolichol and PO3-4 can be explained as the result of product inhibition. An apparent Km-value of 2.5 X 10(-5) M is computed for [1-3H]DMP. Bacitracin inhibits DMP-phosphatase in contrast with other reports. Propylthiouracyl, cAMP, TSH and several other bio-effectors are without effect on the in vitro system. The specificity of the DMP-Pase activity is discussed, showing that the phosphatase is distinctly different from other phosphatases especially phosphatidic acid phosphohydrolase.

Isolation and purification of chloroplastic spinach (Spinacia oleracea) sedoheptulose-1,7-bisphosphatase

Higher-plant sedoheptulose-1,7-bisphosphatase was isolated and purified over 200-fold from spinach (Spinacia oleracea) chloroplast stromal extracts to apparent electrophoretic homogeneity by DEAE-Fractogel, molecular sieving on Sephadex G-200 and Blue B dye-matrix affinity chromatography. It is a protein of Mr 66,000, made up of two apparently identical subunits (Mr 35,000). The enzyme is activated by reduced thioredoxin fb in the presence of dithiothreitol. Its specificity towards sedoheptulose 1,7-bisphosphate versus fructose 1,6-bisphosphate is high, but not absolute.

Metabolism of glycerate 2,3-P2--XII. Characterization of the 2,3-bisphosphoglycerate synthase-phosphatase and of the hybrid phosphoglycerate mutase/2,3-bisphosphoglycerate synthase-phosphatase from pig brain

2,3-Bisphosphoglycerate synthase-phosphatase and the hybrid phosphoglycerate mutase/2,3-bisphosphoglycerate synthase-phosphatase have been partially purified from pig brain. Their 2,3-bisphosphoglycerate synthase, 2,3-bisphosphoglycerate phosphatase and phosphoglycerate mutase activities are concurrently lost upon heating and treatment with reagents specific for histidyl, arginyl and lysyl residues. The two enzymes differ in their thermal stability and sensitivity to tetrathionate. Substrates and cofactors protect against inactivation, the protective effects varying with the modifying reagent. The synthase activity of both enzymes shows a nonhyperbolic pattern which fits to a second degree polynomial. The Km, Ki and optimum pH values are similar to those of the 2,3-bisphosphoglycerate synthase-phosphatase from erythrocytes and the hybrid enzyme from skeletal muscle. The synthase activity is inhibited by inorganic phosphate and it is stimulated by glycolyate 2-P.

A new acylphosphatase isoenzyme from human erythrocytes: purification, characterization, and primary structure

A new acylphosphatase from human erythrocytes was isolated by an original purification procedure. It is an isoenzyme of the well-characterized human skeletal muscle acylphosphatase. The erythrocyte enzyme shows hydrolytic activity on acyl phosphates with higher affinity than the muscle enzyme for some substrates and phosphorylated inhibitors. The sequence was determined by characterizing the peptides purified from tryptic, peptic, and Staphylococcus aureus V8 protease digests of the protein, and it was found to differ in 44% of the total positions as compared to the human muscle enzyme. About one-third of these differences are in the form of strictly conservative replacements. The protein consists of 98 amino acid residues; it has an acetylated NH2-terminus and does not contain cysteine: (sequence in text).

Purification and properties of spinach leaf phosphofructokinase 2/fructose 2,6-bisphosphatase

Phosphofructokinase 2 was purified from spinach leaves by fractionation with poly(ethylene glycol) and by chromatography on blue Sepharose, anion exchanger Mono-Q and blue Trisacryl. A low-Km fructose-2,6-bisphosphatase copurified with phosphofructokinase 2 and its constitutive subunits could be easily identified by sodium dodecyl sulphate gel electrophoresis thanks to the formation of a [32P]phosphoenzyme intermediate upon short-time incubation in the presence of 1 microM fructose 2,6-[2-32P]bisphosphate. On anion-exchange chromatography, two peaks of phosphofructokinase 2/fructose-2,6-bisphosphatase were resolved. The first one, called L (light), represented about 10% of the phosphofructokinase 2 activity and was characterized by a phosphofructokinase 2/fructose-2,6-bisphosphatase activity ratio close to 1, by an Mr of 132,000 as measured by gel filtration, and by a series of subunits of Mr comprised between 44,000 and 70,000. The second and major peak of phosphofructokinase 2, called H (heavy), had a phosphofructokinase 2/fructose-2,6-bisphosphatase ratio close to 8, an Mr of 390,000 and was made of 90,000-Mr subunits. The H form of phosphofructokinase 2 had a lower Km for fructose 6-phosphate than the L form and a higher Ki for a series of physiological inhibitors. By contrast, the kinetics of fructose-2,6-bisphosphatase was the same for the two forms of the enzyme. Upon incubation in the presence of papain or of a crude spinach leaf extract, the purified H form gave rise to products made of subunits of Mr comprised between 70,000 and 44,000 but also of lower values which maintained their fructose-2,6-bisphosphatase activity. The H and L forms of phosphofructokinase 2/fructose-2,6-bisphosphatase were also detected in crude homogenates of castor bean endosperm and of Jerusalem artichoke tubers.

Mu-opioid receptor is associated with phosphatase activity

A preparation of purified mu opioid receptor from bovine brain hydrolyzes p-nitrophenylphosphate. This phosphatase activity has a pH optimum of 9.0, a Km of 9.0 microM, and is stimulated by Mn++ and Mg++ ions. Evidence that the observed activity is not due to a contaminant in the opioid receptor preparation includes 1) the activity is associated primarily with 60,000 molecular weight material which is much smaller than bovine brain alkaline phosphatase; and 2) the activity could not be absorbed by antibodies specific for bovine alkaline phosphatase. Thus this appears to be the first demonstration of enzymatic activity associated with an opioid receptor.

Activation of human erythrocyte 2,3-bisphosphoglycerate phosphatase at physiological concentrations of substrate

In human erythrocytes the reactions of the 2,3-bisphosphoglycerate shunt are catalyzed primarily by one protein, 2,3-bisphosphoglycerate synthase-phosphatase. At low concentrations of 2,3-bisphosphoglycerate the phosphatase is activated by several anions including inorganic phosphate and sulfite, and the phosphate activation is inhibited by low concentrations of 3-phosphoglycerate [Z. B. Rose and J. Liebowitz (1970) J. Biol. Chem. 245, 3232-3241]. Phosphate and sulfite also activate at high but physiological concentrations of 2,3-bisphosphoglycerate (5 mM), but the inhibition by 3-phosphoglycerate is much weaker. The basal activity (without added phosphate or sulfite) was also found to be higher and to be 3-phosphoglycerate sensitive; this is attributed to activation either by 2,3-bisphosphoglycerate itself or by a contaminant in it. These results allow previous observations of 2,3-bisphosphoglycerate hydrolysis in intact erythrocytes to be reconciled with the properties of the purified enzyme under near-physiological conditions.

Isolation and characterization of multiple forms of Mg2+-dependent phosphatidate phosphohydrolase from rat adipose cytosol

In the present studies, we have made several unique observations. First, we have shown that cytosolic phosphatidate phosphohydrolase from adipose tissue subjected to butyl-agarose chromatography was resolved into four different components. These components, designated as passthrough (PT), D150, D250 and E, were present in the proportions of 51:7:24:16, respectively, in the rat adipose cytosol. Comparison of the properties of these components revealed some similar properties, and also several differences. These components showed the same pH optimum, required Mg2+ for activity and were inhibited by N-ethylmaleimide, indicating a requirement of active sulfhydryl groups for activity. These components differed from one another with respect to hydrophobicity, sedimentation behavior, Stokes diameter, Km values, thermolability and susceptibility to proteinase treatment. Second, we have shown that each component of this system was associated with lipids which were found to be essential for the catalytic activity. Perturbation of this association by organic solvent or by adding excess amounts of exogenous lipids resulted in the loss of enzyme activity. Finally, we analyzed lipid composition of individual components. These studies suggest that the multi-component system of Mg2+-dependent phosphatidate phosphohydrolase may be a part of the cytomembrane network.

Purification and properties of phosphofructokinase 2/fructose 2,6-bisphosphatase from chicken liver and from pigeon muscle

Phosphofructokinase 2 and fructose 2,6-bisphosphatase extracted from either chicken liver or pigeon muscle co-purified up to homogeneity. The two homogeneous proteins were found to be dimers of relative molecular mass (Mr) close to 110,000 with subunits of Mr 54,000 for the chicken liver enzyme and 53,000 for the pigeon muscle enzyme. The latter also contained a minor constituent of Mr 54,000. Incubation of the chicken liver enzyme with the catalytic subunit of cyclic-AMP-dependent protein kinase in the presence of [gamma-32P]ATP resulted in the incorporation of about 0.8 mol phosphate/mol enzyme. Under similar conditions, the pigeon muscle enzyme was phosphorylated to an extent of only 0.05 mol phosphate/mol enzyme and all the incorporated phosphate was found in the minor 54,000-Mr constituent. The maximal activity of the native avian liver phosphofructokinase 2 was little affected by changes of pH between 6 and 10. Its phosphorylation by cyclic-AMP-dependent protein kinase resulted in a more than 90% inactivation at pH values below 7.5 and in no or little change in activity at pH 10. Intermediary values of inactivation were observed at pH values between 8 and 10. Muscle phosphofructokinase 2 had little activity at pH below 7 and was maximally active at pH 10. Its partial phosphorylation resulted in a further 25% decrease of its already low activity measured at pH 7.1 and in a negligible inactivation at pH 8.5. Phosphoenolpyruvate and citrate inhibited phosphofructokinase 2 from both origins non-competitively. The muscle enzyme and the phosphorylated liver enzyme displayed much more affinity for these inhibitors than the native liver enzyme. Fructose 2,6-bisphosphatase from both sources had about the same specific activity but only the chicken liver enzyme was activated about twofold upon incubation with ATP and cyclic-AMP-dependent protein kinase. All enzyme forms were inhibited by fructose 6-phosphate and this inhibition was released by inorganic phosphate and by glycerol 3-phosphate. Both liver and muscle fructose 2,6-bisphosphatases formed a 32P-labeled enzyme intermediate when incubated in the presence of fructose 2,6-[2-32P]bisphosphate.

Kinetic properties and essential amino acids of the 2,3-bisphosphoglycerate synthase-phosphatase from pig skeletal muscle

Histidine, arginine and lysine residues are essential for the multifunctional 2,3-bisphosphoglycerate synthase-phosphatase purified from pig skeletal muscle. The synthase, phosphatase and phosphoglycerate mutase activities of the enzyme are concurrently lost upon treatment with diethylpyrocarbonate, phenylglyoxal and trinitrobenzenesulfonate. The phosphatase activity shows hyperbolic kinetics. In contrast, the synthase activity shows a nonhyperbolic pattern which fits to a second-degree polynomial. The Km values for glycerate 1,3-P2, glycerate 3-P and glycerate 2,3-P2 are similar to those of the enzyme from mammalian erythrocytes.

Partial purification of a nucleoside triphosphatase from the inner membrane of the chloroplast envelope of pea

A Mg2+-NTPase has been partially purified from the inner membrane of the pea chloroplast envelope. Isolated envelope membranes were solubilized with Triton X-100 and fractionated by DEAE-Sephadex chromatography, followed by ultrafiltration and sucrose density gradient centrifugation. An approximate 35-fold increase in the specific activity of the vanadate and sodium fluoride sensitive NTPase was obtained. Analysis of the partially purified NTPase by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed a single 37-kDa polypeptide that appeared to be associated with the activity. In support of this identification, it is demonstrated that the 37-kDa polypeptide can be photolabeled with 8-azido-ATP.

Purification and characterization of rabbit muscle acylphosphatase in the thiol (-SH) form

Modifications in the muscle acylphosphatase purification procedure enabled us to isolate the enzyme with its sole cysteine in the -SH form; this enzyme form is the most abundant in vivo. Our data demonstrates that the enzyme forms purified by previously reported procedures can be easily derived from a reaction of the SH-enzyme with oxidized glutathione. Probably most, or even all, of these enzyme forms are artifacts due to the purification. The SH-acylphosphatase shows kinetic parameters similar to those reported for the mixed disulfide with glutathione and S-S dimer, except for the specific activity value, which is about twice as much, and the Km, which is reduced.

NADP phosphatase as a marker in free-flow electrophoretic separations for cisternae of the Golgi apparatus midregion

Based on cytochemical analysis, the enzyme NADP phosphatase is most concentrated in the so-called intercalary cisternae from the mid-region of the Golgi apparatus stack. Using free-flow electrophoresis to separate different Golgi regions of rat liver Golgi apparatus, the NADP phosphatase activity, based on estimation of the rate of release of inorganic phosphate from NADP under standard conditions, was similarly localized to membrane fractions from the center of electrophoretic separations. Peak specific activities for both a putative cis marker (NADH-cytochrome c reductase) and an established trans marker (galactosyltransferase) coincided with minima in NADP phosphatase activity, in agreement with the cytochemical observations. The pattern of distribution of enzyme activity for NADP phosphatase differed from that of both acid phosphatase and glucose-6-phosphatase. The pH optimum was 5.0, the Km for NADP was 0.6 mM and a corresponding production of NAD and inorganic phosphorus was shown. Taken together with other markers for free-flow electrophoresis separation, the NADP phosphatase will provide considerable utility as a specific marker to help identify intercalary cisternae of the mammalian Golgi apparatus and to monitor electrophoretic separations.

Mitochondrial location of rat liver dinucleoside triphosphatase

Rat liver dinucleoside triphosphatase (EC 3.6.1.29) is associated with sucrose-gradient purified mitochondria and can be extracted by freeze and thaw treatment. The proportion of mitochondrial dinucleoside triphosphatase approaches 50% of total liver enzyme. Evidence is also presented that 10% of total liver bis(5'-guanosyl)tetraphosphatase (EC 3.6.1.17) might be equally linked to mitochondria. Those data suggest that diadenosine 5',5'''-P1,P3-triphosphate, diadenosine 5',5'''-P1,P4-tetraphosphate, or other substrates of those enzymes, might be somehow related to mitochondria or mitochondrial function(s), although the occurrence of dinucleoside polyphosphates has not been reported in that organelle.

Purification and characterization of the major nucleoside triphosphatase from rat liver nuclear envelopes

Nuclear envelopes contain a nucleoside triphosphatase. Hydrolysis of ATP or GTP by this enzyme parallels energy-dependent efflux of poly(A)-containing mRNA from nuclei in vitro. Nucleoside triphosphatase has been purified from highly purified preparations of nuclear envelopes from rat liver by three successive affinity steps. The essentially homogeneous enzyme has an apparent molecular weight of 40,000 as checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and displays a rather broad substrate specificity. ATP and GTP are hydrolyzed at nearly equal rates, whereas UTP and CTP are only half as active as substrates. For optimal activity, a one-to-one ratio of a divalent cation (Mg2+, Mn2+, or Ca2+) and the nucleoside triphosphate substrate, an alkaline pH and a temperature of 34 degrees C are required. In contrast to the enzyme associated with nuclear envelopes which is stimulated by synthetic poly(A) and the poly(A) segment of the natural poly(A)-containing mRNA, homogeneous nucleoside triphosphatase is unable to be modulated by this polynucleotide species.

Functional characterization of the enzymes with 2,3-bisphosphoglycerate phosphatase activity from pig skeletal muscle

In pig skeletal muscle exist four enzymes with 2,3-bisphosphoglycerate phosphatase activity. Two of them (forms I-A and I-C) are multi-functional enzymes which, in addition to the phosphatase activity, possess 2,3-bisphosphoglycerate synthase and phosphoglycerate mutase activities. The other two enzyme forms (II-A and II-B) only show the phosphatase activity. The four enzymes differ in substrate specificity. Form I-C is highly specific for glycerate 2,3-P2; form I-A also hydrolyzes the monophosphoglycerates and forms II-A and II-B are specific for phosphoester bonds adjacent to a C-1 carboxylic group. The enzymes possess similar Km, Kcat and optimum pH value, but they are differently inhibited by the reaction products. They are also differently affected by glycolate-2-P (their main activator) and by other modifiers. Probably form I-A, which corresponds to M-type phosphoglycerate mutase, is the main enzyme implicated in the breakdown of glycerate 2,3-P2 in pig muscle.