Trehalose-phosphate synthase of Mycobacterium tuberculosis. Cloning, expression and properties of the recombinant enzyme.

The trehalose-phosphate synthase (TPS) of Mycobacterium smegmatis was previously purified to apparent homogeneity and several peptides from the 58 kDa protein were sequenced. Based on that sequence information, the gene for TPS was identified in the Mycobacterium tuberculosis genome, and the gene was cloned and expressed in Escherichia coli with a (His)6 tag at the amino terminus. The TPS was expressed in good yield and as active enzyme, and was purified on a metal ion column to give a single band of approximately 58 kDa on SDS/PAGE. Approximately 1.3 mg of purified TPS were obtained from a 1-L culture of E. coli ( approximately 2.3 g cell paste). The purified recombinant enzyme showed a single band of approximately 58 kDa on SDS/PAGE, but a molecular mass of approximately 220 kDa by gel filtration, indicating that the active TPS is probably a tetrameric protein. Like the enzyme originally purified from M. smegmatis, the recombinant enzyme is an unusual glycosyltransferase as it can utilize any of the nucleoside diphosphate glucose derivatives as glucosyl donors, i.e. ADP-glucose, CDP-glucose, GDP-glucose, TDP-glucose and UDP-glucose, with ADP-glucose, GDP-glucose and UDP-glucose being the preferred substrates. These studies prove conclusively that the mycobacterial TPS is indeed responsible for catalyzing the synthesis of trehalose-P from any of the nucleoside diphosphate glucose derivatives. Although the original enzyme from M. smegmatis was greatly stimulated in its utilization of UDP-glucose by polyanions such as heparin, the recombinant enzyme was stimulated only modestly by heparin. The Km for UDP-glucose as the glucosyl donor was approximately 18 mm, and that for GDP-glucose was approximately 16 mm. The enzyme was specific for glucose-6-P as the glucosyl acceptor, and the Km for this substrate was approximately 7 mm when UDP-glucose was the glucosyl donor and approximately 4 mm with GDP-glucose. TPS did not show an absolute requirement for divalent cations, but activity was increased about twofold by 10 mm Mn2+. This recombinant system will be useful for obtaining sufficient amounts of protein for structural studies. TPS should be a valuable target site for chemotherapeutic intervention in tuberculosis.     

Purification of Xyloglucan Hydrolase/Endotransferase from Cell Walls of Azuki Bean Epicotyls

An enzyme involved in the breakdown of xyloglucans was purifiedfrom an extract of cell walls of azuki bean epicotyls obtainedwith 1 M NaCl and purified by column chromatography on severaldifferent resins. The purified enzyme gave a single band ofa protein with a molecular mass of about 32 kDa after SDS-PAGE.The enzyme hydrolyzed the xyloglucans of high molecular massfrom azuki cell walls to yield fragments of about 50 kDa withoutproduction of any oligo- or monosaccharides. Moreover, the enzymehad hardly any effect on xyloglucans of less than 60 kDa. Theenzyme also hydrolyzed xyloglucans from tamarind, but it didnot react with cellulose derivatives. In the presence of pyridylamino-labeledxyloglucan oligosac-charides as acceptor substrates, the enzymecatalyzed the transfer of 50-kDa products to the oligosaccharides.The K_m value of the enzyme for xyloglucans of 540 kDa was similarin the presence and in the absence of xyloglucan oligosaccharidesas acceptors: 1.0 mg ml^–1. These results suggest thatthe enzyme was an endotransferase but had unusual acceptor specificity,preferring smaller acceptors such as water. (Received September 9, 1996; Accepted March 16, 1997)     

Structural and Kinetic Properties of NADP-Malic Enzyme from the Inducible Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum L.

NADP-malic enzyme (EC 1.1.1.40 [EC] ), which is involved in Crassulaceanacid metabolism (CAM), was purified to electrophoretic homogeneityfrom the leaves of the inducible CAM plant Mesembryanthemumcrystallinum. The NADP-malic enzyme, which was purified 1,146-fold,has a specific activity of 68.8 µmol (mg protein)^–1min^–1. The molecular weight of the subunits of the enzymewas 64 kDa. The native molecular weight of the enzyme was determinedby gel-filtration to be 390 kDa, indicating that the purifiedNADP-malic enzyme is a hexamer of identical subunits. The optimalpH for activity of the enzyme was around 7.2. Double-reciprocalplots of the enzymatic activity as a function of the concentrationof L-malate yielded straight lines both at pH 7.2 and at pH7.8 and did not reveal any evidence for cooperativity of bindingof L-malate. The K_m value for L-malate was 0.35 mM. Hill plotsof the activity as a function of the concentration of NADP⁺indicated positive cooperativity in the binding of NADP⁺ tothe enzyme with a Hill coefficient (nH) of 2.0. An S_0.5 value(the concentration giving half-maximal activity) of 9.9 µMfor NADP⁺ was obtained. Oxaloacetate inhibited the activityof the NADP-malic enzyme. Effects of succinate and NaHCO₃ onthe activity of NADP-malic enzyme were small. (Received October 30, 1991; Accepted May 1, 1992)     

Biochemical properties of 1-aminocyclopropane-1-carboxylate N-malonyltransferase activity from early growing embryonic axes of chick-pea (Cicer arietinum L.) seeds

In the present work, certain biochemical characteristics ofthe enzyme 1-aminocyclopropane-1-carboxylate N-malonyltransferase(ACC N-MTase) which is responsible for the malonylation of 1-aminocyclopropane-1-carboxylate(ACC) in chickpea (Cicer arietinum) are described. Phosphatebuffer was the most appropriate buffer with regard to enzymestability and, therefore, ACC N-MTase was extracted, assayedand purified in the presence of this buffer. ACC N-MTase waspartially purified approximately 900-fold from embryonic axesof chick-pea seeds using ammonium sulphate precipitation, hydrophobicinteraction and molecular filtration chromatography. By gelfiltration chromatography on Superose-12, the molecular massof the enzyme was estimated to be 54 4 kDa. ACC N-MTase hadan optimal pH and temperature of 7.5 and 40C, respectively,as well as a K_m for ACC and malonyl-CoA of 400 M and 90 M,respectively. D-Phenylalanine was a competitive inhibitor ofACC N-MTase with respect to ACC (K_i of 720 M), whereas co-enzymeA was a competitive product inhibitor with respect to malonyl-CoA(K_i of 300 M) and a non-competitive inhibitor with respectto ACC (K_i of 600 M). Under optimal assay conditions, ACC N-MTasewas strongly inhibited by (a)divalent [Zn²⁺>Mg²⁺>>Co²⁺>Co²⁺>(NH₄)²⁺>Fe²⁺]and monovalent metal cations (Li⁺>Na⁺>K⁺), without activitybeing detected in the presence of Hg²⁺, and (b) PCMB or mersalicacid, suggesting that sulphydryl group(s) are involved at theactive site of the enzyme. Key words: ACC-N-malonyltransferase, Cicer arietinum, embryonic axes, ethylene, germination, seeds     

Comparative Studies of NAD-Malic Enzyme from Leaves of Various C4 Plants

Using butyl-TSK-gel chromatography, we purified NAD-malic enzyme(ME) (EC 1.1.1.39 [EC] ), which is involved in C₄ photosynthesis,to electrophoretic homogeneity, from leaves of Amaran-thus tricolor.Molecular weights of the native and SDS-denatured enzyme fromA. tricolor were 490 kDa and 61 kDa, respectively. During assayof the enzyme there was a slow reaction transient in the formof a lag before a steady-state rate was reached. The durationof this lag was inversely proportional to the concentrationof each substrate and the activator, fructose- 1,6-bis-phosphate(FBP). The optimal pH of the reaction fell with decreasing concentrationsof either malate or FBP. High pH prolonged the lag in reaction. Double reciprocal plots of the enzymatic activity as a functionof the concentration of malate yielded straight lines and didnot show any cooperativity for binding of malate. The enzymefrom A. tricolor was not inhibited by either HCO^–₃ orCO₂. At different concentrations of malate, the nature of theactivating effect of FBP was compared among the purified enzymesfrom A. tricolor and the C₄ monocots Eleusine coracana and Panicumdichotomiflorum. At low levels of malate, FBP markedly stimulatedthe enzyme from each species. In contrast, at saturating levelsof malate, the response of enzymes to increasing concentrationsof FBP was different and depended on the source of enzyme. The immunochemical properties of the enzymes from the threespecies were compared using an enzyme-linked immunoadsorbentassay with antisera raised against the purified enzymes fromthe three species. Different cross-reactivities were observedamong the enzymes from different sources. The N-terminal aminoacid sequences of NAD-MEs from the three species were determinedand some differences were found among the three enzymes. ²Permanent address; Tohoku National Agricultural ExperimentStation, Morioka, 020-01 Japan. ³Permanent address; National Grassland Research Institute, Nishinasuno,Tochigi, 329-27 Japan. (Received December 12, 1988; Accepted February 17, 1989)     

Detection and Characterization of UDP-Glucose:Flavonoid O-Glucosyltransferases in the Leaves of Prunus ? yedoensis Matsum

A novel O-glucosyltransferase (I4'GT) which catalyzes the transferof D-glucose from UDP-D-glucose to position 4' of prunetin (4',5-dihydroxyl-7-methoxyisoflavone)was isolated from the leaves of Prunus ? yedoensis Matsum. andpurified 66-fold by precipitation with ammonium sulfate andchromatography on DEAE-cellulose. UDP-glucose:flavonol 3-O-glucosyltransferase(F3GT) was also isolated and purified 50-fold in the same manner.The molecular weights of both I4'GT and F3GT were estimatedby elution from a column of Sephadex G-100 to be about 51,000Da. The pH optima for I4'GT and F3GT activities were 8.0 and7.5, respectively. The specificities of I4'GT and F3GT for thesugar donor were quite strict, and only UDP-glucose could serveas glucosyl donor, both ADP-D-glucose and GDP-D-glucose beingineffective. The apparent K_m values for UDP-glucose and prunetinwere 10.0µM and 1.20µM, respectively, for I4'GT.The K_m values for UDP-glucose and quercetin were 9.8 µMand 1.21 µM, respectively, for F3GT. The activities ofboth I4'GT and F3GT were stimulated by 1 mM Mg*⁺ and stronglyinhibited by 1 mM Cu²⁺, 1 mM Zn²⁺ and various reagents thatreact with sulfhydryl groups. (Received May 16, 1990; Accepted September 3, 1990)     

Enzymic mechanism of starch breakdown in germinating rice seeds V. Sucrose phosphate synthetase in the scutellum

Some enzymic Properties of a partially purified preparationof sucrose phosphate synthetase (E.C.2.4.1.14) from germinatingrice seed scutella were studied. Examination of the reactionkinetics revealed that the rate of synthesis of sucrose phosphatefollows the Michaelis-Menten equation at an optimum PH of 7.5,having K_m of 25 mM for UDP-glucose, and of 4.9 mM for fructose6-phosphate. UDP inhibited the enzyme reaction competitively;K₁ of 3.3 mM. Fe⁺⁺ and Fe⁺⁺⁺ activated the enzyme reaction about2-fold; K_a, 0.3 mM and 2.0 mM, respectively. Co⁺⁺, Co(NH₃)₆⁺⁺⁺,Mg⁺⁺ and Mn⁺⁺ also activated the enzyme reaction. At high concentrationK⁺ activated the enzyme reaction with the maximum activationof 24% at 400 mM. The molecular weight and S_20,w value of theenzyme were determined as 4.5 ? 10⁵ and 10.4S, respectively. ¹Part IV of this series is Ref. (5). ²California Foundation for Biochemical Research Fellow (1973). (Received December 20, 1973; )     

Purification, Properties and Phosphorylation of Anaerobically Induced Enolase in Echinochloa phyllopogon and E. crus-pavonis

Enolase (2-phospho-D-glycerate hydrolyase, EC 4.2.1.11 [EC] ) activityis differentially induced by anoxia in the flood-tolerant speciesE. phyllopogon (Stev.) Koss and the flood-intolerant speciesE. crus-pavonis (H.B.K.) Schult. To examine the regulation ofenolase at the protein level, we purified the enzyme from bothspecies to near homogeneity and compared their physico-chemicaland catalytic properties. Enolase purified from E. phyllopogonexhibits optimal activity at pH 7.0, a K_m of 80 µM for2-PGA, a Q₁₀ of 1.97 and an E_a of 12.3 kcal mol^-1. Similarly,enolase from E. crus-pavonis exhibits optimal activity at pH7.0, a K_m of 50 µM for 2-PGA, a Q₁₀ of 2.04 and an E_aof 12.9 kcal mol^-1. The enzyme from both species is thermostable(100% active after 15 min, 50°C) and is a homodimer of 52.5kDa subunits as resolved by SDS-PAGE and immunoblotting. E.phyllopogon enolase was phosphorylated in vitro using either[     

Purification and properties of DNA topoisomerase II from Daucus carota cells

Topoisomerase II was partially purified from Daucus carota cellsby a procedure including ammonium sulphate fractionation, ion-exchange,and affinity chromatography steps. The type II enzyme, identifiedfor its ability to unknot knotted P4 DNA and decatenate Trypanosomacruzi kDNA, requires ATP and Mg²⁺ for activity. The unknottingactivity was sensitive to an inhibitor of the mammalian typeII enzyme, the drug VP16 (IC₅₀ 32 mmol m^–3), whereas inhibitorsof DNA gyrase showed a limited effect on activity. The SDS-PAGEanalysis of the dsDNA cellulose fraction revealed the presenceof four polypeptides of apparent molecular masses of 72, 71,34, and 33 kDa among which only a polypeptide of about 70 kDacrossreacted with antibodies against yeast topoisomerase II.Immunoprecipitation experiments with monoclonal antibodies tothe and ß isoforms of the human enzyme confirmedthe recognition of a polypeptide of 70 kDa. The sedimentationcoefficient (S) of the topoisomerase II in the phosphocellulosefraction, calculated by analytical glycerol gradient, was 6.1corresponding to a molecular mass of about 123 kDa. Resultssuggest the presence in carrot of a protein of molecular massof 70 kDa having the typical properties of an eukaryotic topoisomeraseII and carrying epitopes recognized by MoAbs to both human and ß enzymes. The 70 kDa polypeptide might then representthe monomer of a homodimer enzyme of 123 kDa. Key words: Daucus carota, topoisomerase II, immunoprecipitation     

Biosynthesis of Xyloglucan in Suspension-cultured Soybean Cells. Evidence that the Enzyme System of Xyloglucan Synthesis does not Contain {beta}-1,4-Glucan 4-{beta}-D-Glucosyltransferase Activity (EC 2.4.1.12)

Xyloglucan 4-ß-D-glucosyltransferase, an enzyme responsiblefor the formation of the xyloglucan backbone, in a particulatepreparation of soybean cells has been compared with ß-1,4-glucan4-ß-D-glucosyltransferase of the same origin. Thefollowing observations indicate that the enzyme system of xyloglucansynthesis does not contain ß-1,4-glucan 4-ß-D-glucosyltransferaseactivity, although both enzymes transfer the glucosyl residuefrom UDP-glucose to form the ß-1,4-glucosidic linkage:1. The incorporation of [¹⁴C]glucose into xyloglucan dependedon the presence of UDP-xylose in the incubation mixture. 2.No measurable amount of radioactivity was incorporated fromUDP-[¹⁴C]xylose into the cello-oligosaccharides, although theincorporation of [¹⁴C]xylose into xyloglucan depended on thepresence of UDP-glucose in the incubation mixture (Hayashi andMatsuda 1981b). 3. The activity of xyloglucan 4-ß-D-glucosyltransferasewas stimulated more strongly by Mn²⁺ than by Mg²⁺, whereas Mg²⁺was the most active stimulator for the activity of ß-1,4-glucan4-ß-D-glucosyltransferase. 4. An addition of GDP-glucose(100 µM) to the incubation mixture inhibited the activityof xyloglucan 4-ß-D-glucosyltransferase by 17%, whereasthe activity of ß-1,4-glucan 4-ß-D-glucosyltransferasewas inhibited 56% under the same conditions. 5. Irpex exo-cellulasedid not hydrolyze the xyloglucan synthesized in vitro. 6. Theß-1,4-glucan synthesized in vitro was not a branchedxyloglucan because it gave no 2,3-di-O-methyl glucose derivativeon methylation analysis. 7. Pulse-chase experiments indicatedthat the ß-1,4-glucan was not transformed into thexyloglucan. The subcellular distribution of the xyloglucan synthase, however,was similar to that of the ß-1,4-glucan synthase (Golgi-located1,4-ß-D-glucan 4-ß-D-glucosyltransferase).Thus, it appears that the latter enzyme is located at a siteclose to xyloglucan synthase and is set aside for the assemblyof these polysaccharides into the plant cell surface. (Received May 21, 1981; Accepted October 13, 1981)     

Inactivation of 1-aminocyclopropane-1-carboxylate (ACC) oxidase

The enzyme 1-aminocyclopropane-1-carboxylate (ACC) oxidase,which catalyses the final step in the biosynthesis of ethylene,showed a non-linear time-course in vitro and activity decayedwith a half-life of around 14 min. This loss of activity wasstudied using tomato ACC oxidase purified from Escherichia coiltransformed with the cDNA clone pTOM13. Inactivation was notdue to end-product inhibition by dehydroascorbic acid or cyanide.Preincubatlon of enzyme in the combined presence of Fe²⁺ ascorbateand ACC, which together allowed catalytic turnover, resultedin almost total loss of ACC oxidase activity. Enzyme Inactivatedby catalysis could not be reactivated by passage through SephadexG-25 or by treating with combina tions of DTT and CO₂ A non-lineartime-course and inactivation in the presence of all substratesand cofactors was also shown for the enzyme assayed in vivowith melon fruit discs. Using the purified tomato enzyme a distinctascorbate-dependent inactivation was also observed, which occurredIn the absence of catalysis and was prevented, although notreversed, by catalase. This ascorbate-dependent inactivationmay thus be due to H₂O₂ attack on ACC oxidase. Key words: 1-aminocyclopropane-1-carboxylate (ACC) oxidase, catalase, catalytic inactivation, ethylene     

Purification of Ribulose 5-phosphate Kinase and Minor Polypeptides of Pyrenoid from the Green Alga Bryopsis maxima

Ribulose 5-phosphate (Ru5P) kinase (ATP:D-ribulose 5-phosphate1-phosphotrans- ferase; EC 2.7.1.19 [EC] ), an enzyme in the reductivepentose phosphate cycle, was purified from the green alga Bryopsismaxima and its activity and peptide composition were studied.The specific activity of purified Ru5P kinase was 20 µmoleRuBP formed (mg protein)^–1 min^–1 corresponding toa 490-fold purification from the supernatant of chloroplasts.The K_m values of Ru5P kinase for ATP and Ru5P were 69 µMand 330 µM, respectively. The molecular size of Ru5P kinase was estimated as 90 kDa bygel filtration and that of its polypeptide as 41 kDa by SDS-polyacrylamidegel electrophoresis. A small portion of the Ru5P kinase wasfound in a large molecular state (500 kDa) which was consideredto be an inactive form of the enzyme. Ru5P kinase activity has been reported in the pyrenoid of Eremosphaeraviridis as well as ribulose 1,5-bisphosphate carboxylase-oxygenase(RuBisCO) and ribose 5-phosphate isomerase activity (Holdsworth1971). In Bryopsis maxima, among the pyrenoid polypeptides otherthan that of RuBisCO, we found a polypeptide of 42 kDa, similarto that of Ru5P kinase in molecular size and ratio to RuBisCO.A peptide map of the 42 kDa pyrenoid polypeptide, however, showedthat it differed from that of Ru5P kinase. In conclusion, Ru5Pkinase may be not involved in the pyrenoid of this alga. (Received January 19, 1985; Accepted May 15, 1985)     

Intracellular Localization and Properties of NADH-Glutamate Dehydrogenase from Vitis vinifera L.: Purification and Characterization of the Major Leaf Isoenzyme

Glutamate dehydrogenase was partially purified from grapevine(Vitis vinifera L. cv. Soultanina) tissues and its activityand isoenzymic pattern were studied. Seven anodal migratingisoenzymes were revealed after PAGE. Leaf protoplasts were isolatedfrom in vitro-grown axenic shoot cultures and used to studythe intracellular localization of GDH. Results revealed thatthe enzyme was associated with the mitochondrial fraction. Theisoenzyme with the lowest electrophoretic mobility, which accountedfor 35 to 40% of total activity, was purified 2050-fold to homogeneityfrom leaves. The purification method included ammonium sulphatefractionation, DEAE-cellulose chromatography, Sephadex G-200gel filtration and NAD-sepharose affinity chromatography. Themolecular weight of the native enzyme was estimated to be 252kDa and it consisted of identical 42.5 kDa subunits. pH optimumfor the aminating reaction was 8.0 and for the deaminating reaction9.3. At optimum pH conditions the apparent K_m values for ammonium,as ammonium chloride and ammonium sulphate, -ketoglutarate,NADH, glutamate, and NAD⁺ were 45.0, 13.0, 2.1, 0.069, 18.0,and 0.195 mM, respectively. The amination reaction of GDH wasfully activated with about 100 µM Ca²⁺ while the deaminationreaction was not affected by the addition of Ca²⁺. The isoenzymesof GDH showed different magnitude of their activating responseto calcium ions. Key words: Vitis vinifera L., glutamate dehydrogenase     

STUDIES ON HOMOSERINE DEHYDROGENASE IN PEA SEEDLINGS

Partially purified homoserine dehydrogenase was prepared frompea seedlings. The optimum pH for this enzyme is approximately 5.4. The K_mvaluesfor ASA and TPNH are 4.6xl0^–4Af and 7.7xl0^–5M, respectively.This enzyme can also utilize DPNH but less effectively thanTPNH. In contrast with yeast homoserine dehydrogenase whichis insensitive to — SH reagents, the pea enzyme is inhibitedalmost completely by 10^–4MPCMB and 10^–5MHgCl₂, theinhibition being removed by 10^–2M thioglycolate. Homoserinedehydrogenase was found not only in decotylized seedlings, butalso in cotyledons. The significance of this enzyme in homoserine biosynthesis ingerminating pea seeds has been discussed. (Received February 20, 1961; )     

PLA2 stimulation of Na+/H+ antiport and proliferation in rat aortic smooth muscle cells

The proliferative properties and the ability to stimulate theNa⁺/H⁺antiport activity of a secretory phospholipaseA₂ were studied in rat aorticsmooth muscle cells in culture. The requirement of the enzymaticactivity of phospholipase A₂ toelicit mitogenesis was assessed by the use of ammodytin L, aSer⁴⁹ phospholipaseA₂ from the venom ofVipera ammodytes, devoid of hydrolyticactivity. We propose that the proliferative effect is mediated by thesame transduction pathway for both proteins. In particular,1) both secretory phospholipaseA₂ and ammodytin L stimulatedthymidine incorporation in a dose-dependent manner; 2) both proteins affected the cellcycle, as assessed by cell growth and fluorescence-activated cellsorting experiments; 3) bothphospholipase A₂ and ammodytin Lincreased intracellular pH, a permissive factor for cell proliferation,through activation of theNa⁺/H⁺antiport; 4) ammodytin L was able todisplace the ¹²⁵I-labeledphospholipase A₂ from specificbinding sites in a concentration range consistent with that capable ofeliciting a cellular response; and5) the inhibition by heparin wassimilar for both proteins, taking into account the ratio of heparin toprotein. In conclusion, the enzymatic activity of phospholipaseA₂ is not required for thestimulation of mitogenesis. The inhibitory effect of heparin combinedwith its therapeutic potential could help to clarify the role ofphospholipase A₂ in thepathogenesis of several preinflammatory situations.

     

Inhibition by 1-Aminocyclobutane-l-Carboxylate of the Activity of 1-Aminocyclopropane-l-Carboxylate Oxidase Obtained from Senescing Petals of Carnation {Dianthus caryophyllus L.) Flowers

We partially purified 1-aminocyclopropane-l-carboxy-late (ACC)oxidase from senescing petals of carnation {Dianthus caryophyllusL. cv. Nora) flowers and investigated its general characteristics,and, in particular, the inhibition of its activity by ACC analogs.The enzyme had an optimum pH at 7-7.5 and required Fe²⁺, ascorbateand NaHCO₃ for its maximal activity. The K_m for ACC was calculatedas 111-125 µM in the presence of NaHCO₃. Its M_r was estimatedto be 35 and 36 kDa by gel-filtration chromatography on HPLCand SDS-PAGE, respectively, indicating that the enzyme existsin a monomeric form. These properties were in agreement withthose reported previously with ACC oxidases from different planttissues including senescing carnation petals. Among six ACCanalogs tested, l-aminocyclobutane-l-carboxylate (ACBC) inhibitedmost severely the activity of ACC oxidase from carnation petals.ACBC acted as a competitive inhibitor with the K_i of 20-31 µM.The comparison between the K_m for ACC and the K_i for ACBC indicatedthat ACBC had an affinity which was ca. 5-fold higher than thatof ACC. Whereas ACC inactivated carnation ACC oxidase in a time-dependentmanner during incubation, ACBC did not cause the inactiva-tionof the enzyme. Preliminary experiments showed that ACBC andits N-substituted derivatives delayed the onset of senescencein cut carnation flowers. (Received August 19, 1996; Accepted November 26, 1996)     

Effects of Gibberellic Acid on the Activation, Synthesis, and Release of Acid Phosphatase in Barley Seed

Acid phosphatase activity was present in unimbibed barley seed,but rose during incubation of embryoless half-seeds and isolatedaleurone layers, and was further increased by 10^–6 M gibberellicacid (GA₃). Release of total acid phosphatase activity fromhalf-seeds and aleurone layers was markedly enhanced by GA₃.Inhibitor studies with cycloheximide and actinomycin D suggestedthat de novo synthesis of acid phosphatase occurred followingimbibition. Gel nitration, electrophoresis, and [¹⁴C]leucineincorporation studies revealed that a single molecular formof acid phosphatase was present in dry seed, whereas on incubationtwo further forms arose. A proportion of the three molecularforms of the enzyme was synthesized de novo. Gibberellic acidstimulated activation, but not de novo synthesis, of all threemolecular forms of acid phosphatase. Although a small amountof one of the molecular forms was secreted in the absence ofGA₃, the presence of gibberellin greatly increased secretionof the same form of acid phosphatase.     

Purification and some properties of phosphomannomutase from corms of Amorphophallus konjac C. Koch

Phosphomannomutase [Glazer et al.: Biochim. Biophys. Acta 33:522–625 (1959)] was purified 1700-fold in a 39% yieldfrom cell-free extract of konjak (Amorphophallus konjac C. Koch)corms. The molecular weight of the enzyme as determined by gelfiltration was about 62,000. The enzyme required both Mg²+ and-D-glucose-l,6-bisphosphate for activity, although Mg²+ waspartially replaceable by either Co²+ or Ni²+. An apparent equilibriumconstant, K_eq=(mannose-6-phosphate) (mannose-1-phosphate), wasdetermined to be 8.5. Activity was maximal at pH 6.5 to 7.0.Activation energy was 11.1 kcal/mole. The enzyme was the moststable at pH 7.5. The addition of substrate or cofactor markedlyincreased enzyme stability toward heat denaturation. The enzymewas more labile to heat than phosphoglucomutase from konjakcorms. Treatment with various metal ions in Tris buffer inhibited theenzyme. Cu²+ and Zn²+ were the most potent inhibitors amongthe metal ions tested, while Co²+ and Ni²+ were weak. When theenzyme was treated with metal ions in the presence of histidinebuffer, Cu²+ and Zn²+ showed no inhibitory effect on the enzyme,whereas Be²+ inhibited it to an extent similar to that in Trisbuffer. Plots of 1/v versus l/(mannose-l-phosphate) at different fixedconcentrations of glucose-1,6-bisphosphate and 1/v versus 1/(glucose-1,6-bisphosphate)at different fixed concentrations of mannose-1-phosphate wereseries of converging lines. Mannose-1-phosphate at high concentrationswas found to inhibit the enzyme competitively with respect toglucose-l,6-bisphosphate. Apparent K_m and K₁ values for mannose-1-phosphatewere calculated to be 0.2 mM and 1.2 mM, respectively. The K_mvalue for glucose-1,6-bisphosphate was 1.8 µM. ¹This paper constitutes part 5 of a series of studies on konjakmannan biosynthesis. (Received May 24, 1976; )     

A sulfite-dependent adenosine triphosphatase of Thiobacillus thiooxidans. Its partial purification and some properties

A sulfite-dependent ATPase [EC 3.6.1.3 [EC] ] of Thiobacillus thiooxidanswas activated and solubilized by treatment with trypsin [EC3.4.4.4 [EC] ], and purified 84-fold with a 32% recovery. It requiredboth Mg²⁺ and SO₃^2– for full activity, and its optimumpH was found at 7.5–8.0. Mn²⁺, Co²⁺, and Ca²⁺ could partiallysubstitute for Mg²⁺, while SeO₃^2– and CrO₄^2– couldpartially substitute for SO₃^2–. The enzyme hydrolyzed ATP and deoxy-ATP most rapidly and otherphosphate esters were poorer substrates. The apparent Km valuefor ATP was 0.33 mM. The enzyme activity was strongly inhibitedby 0.2 mM NaN₃ and 10 mM NaF. (Received July 27, 1977; )     

Purification and properties of a dissimilatory nitrite reductase of a denitrifying phototrophic bacterium

Nitrite reductase [nitric-oxide : (acceptor) oxidoreductase,EC 1.7.2.1 [EC] ] from a denitrifying phototrophic bacterium, Rhodopseudomonassphaeroides forma sp. denitrificans, was purified. The molecularweight of the enzyme, estimated by gel-filtration, was 80,000.Sodium dodecyl sulfate polyacrylamide gel electrophoresis ofthe purified enzyme showed a single 39,000 molecular weightband, indicating that the enzyme was composed of two subunitsof identical molecular weight. The oxidized form of the enzymeexhibited maximum absorption at 280 nm, 450 nm and 590 nm, andthe reduced form only at 280 nm. The ESR spectrum of a frozensolution of the oxidized enzyme showed a typical spectrum patternof a copper protein, suggesting that two types of Cu²⁺ existedwithin the enzyme. Estimates with an atomic absorption spectrophotometer,revealed two copper atoms per molecule. The optimum pH of theenzyme was 7.0. Km for nitrite was estimated to be 51 µM,and the optimum temperature, 30?C. The enzyme was inhibitedby CO, potassium cyanide and diethyldithiocarbamate and activatedby monoiodoacetate. Phenazine methosulfate, 2,6-dichlorophenolindophenol,horse heart cytochrome c, and cytochrome c₂ from this bacteriumwere suitable electron donors. The enzyme also showed cytochromec oxidase activity. (Received May 4, 1978; )