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1.
In the present paper, we report on the effect of pH and carbonate on the hydrolysis rate constants of N-blocked and free aminoacyl adenylate anhydrides. Whereas the hydrolysis of free aminoacyl adenylates seems principally catalyzed by OH-, the hydrolysis of the N-blocked species is also catalyzed by H+, giving this compound a U-shaped hydrolysis vs. pH curve. Furthermore, at pH's less than 8, carbonate has an extreme catalytic effect on the hydrolysis of free aminoacyl-AMP anhydride, but essentially no effect on the hydrolysis of N-blocked aminoacyl-AMP anhydride. Furthermore, the N-blocked aminoacyl-AMP anhydride is a very efficient generator of peptides using free glycine as acceptor. The possible significance of the observations to prebiological peptide synthesis is discussed. 相似文献
2.
James C. Lacey Jr. Nalinie Senaratne Dail W. Mullins Jr. 《Origins of life and evolution of the biosphere》1984,15(1):45-54
We have used a novel spectrophotometric method to study the hydrolysis of N-acetylphenylalanyl adenylate anhydride (AcPhe-AMP) and phenylalanyl-adenylate anhydride (Phe-AMP) at low concentrations (10–5 M), 25 °C, constant buffer concentration (0.05 M), and as a function of pH. While Phe-AMP is susceptible principally to attack by OH–, with two different rates depending on whether the -amino group of the amino acid is protonated or not, the AcPhe-AMP is susceptible to acid decomposition as well. At pH's 4–8, the Phe-AMP hydrolyzes faster than the AcPhe-AMP, but at pH less than 4 or pH greater than 8, the blocked form hydrolyzes faster. Both forms are also attacked by H2O, and at the same rate. Moreover, the hydrolysis of Phe-AMP is shown to be greatly catalyzed by carbonate, although the AcPhe-AMP is not subject to such catalysis. The rate laws for the various mechanisms and the activation energies for the hydrolyses at pH 7.1 are given. 相似文献
3.
The hydrolyses of p-nitrotrifluoroacetanilide catalyzed by water and imidazole were examined at 70°C. The pH-rate constant profile of the hydrolysis in H2O was examined in the pH range 0.0–11.4. The hydrolysis was independent of pH in the region from pH 1.0 to 4.5, presumably a water-catalyzed reaction. The rate constant and the D2O solvent isotope effect for this reaction were 1.0 × 10?4 sec?1 and 3.7, respectively. Both natural imidazole and imidazolium cation catalyzed hydrolysis. The rate constant of the hydrolysis catalyzed by neutral imidazole was determined to be 5.4 × 10?3M?1 sec?1 and the D2O solvent isotope effect was 1.8. 相似文献
4.
Standard free energy maps for the hydrolysis of ATP as a function of pH and metal ion concentration: comparison of metal ions 总被引:1,自引:0,他引:1
The observed equilibrium constant Kobs for the hydrolysis of ATP to ADP and inorganic phosphate has been calculated as a function of pH and metal ion concentration pM (- log [M]) at 25 °C and μ = 0.2 with the use of literature values of the acid dissociation and complex dissociation constants for the phosphates.The resulting standard free energy changes ΔG °′ are presented by means of contour diagrams for the range pH 4–10 and pM 1–7. These maps summarize the results of some 1900 calculations per diagram, and clearly simulate a differential effect of the metal ions of interest, including Mg2+, Ca2+, Sr2+, Mn2+, Li+, Na+ and K+, on the equilibrium hydrolysis of ATP. 相似文献
5.
Rodrigo Lira de Oliveira Marcos Fellipe da Silva Attilio Converti Tatiana Souza Porto 《Biotechnology progress》2019,35(6):e2879
This study reports on the biochemical characterization as well as the kinetic and thermodynamic study of Aspergillus tamarii URM4634 β-fructofuranosidase (FFase) with transfructosylating activity. Conditions for FFase activity were optimized by means of a central composite rotational design using pH and temperature as the independent variables, while residual activity tests carried out in the temperature range of 45–65°C enabled us to investigate FFase thermostability and estimate the kinetic and thermodynamic parameters of enzyme denaturation. Optimal conditions for sucrose hydrolysis and fructosyl transfer catalyzed by crude FFase were 50°C, and pH 6.0 and 7.4, respectively. The thermodynamic properties of irreversible enzyme inactivation were found to be activation energy of 293.1 kJ mol−1, and activation enthalpy, entropy, and Gibbs free energy in the ranges 290.3–290.4 kJ mol−1, 568.7–571.0 J mol−1 K−1, and 97.9–108.8 kJ mol−1, respectively. The results obtained in this study point out satisfactory enzyme activity and thermostability at temperatures commonly used for industrial fructo-oligosaccharide (FOS) synthesis; therefore, this novel FFase appears to be a promising biocatalyst with great potential for long-term FOS synthesis and invert sugar production. To the best of our knowledge, this is the first report on kinetic and thermodynamic parameters of an A. tamarii FFase. 相似文献
6.
The standard Gibbs free energy change of hydrolysis of α-d-ribose 1-phosphate has been measured at pH 7.0, ionic strength 0.1 m, and 25 °C by combining the corresponding values of the two following reactions: adenosine + H2O ág adenine + ribose (ΔG0′ = ?2.3 ± 0.1 kcal/mol), catalyzed by adenosine nucleosidase, and ribose 1-phosphate + adenine ág adenosine + Pi (ΔG0′ = ?3.1 ± 0.1 kcal/mol), catalyzed by adenosine phosphorylase. The standard Gibbs free energy changes were calculated for both reactions from the equilibrium constant. A value of -5.4 ± 0.15 kcal/mol, comparable to that of other hemiacetal phosphoric esters, was obtained for the hydrolysis of ribose 1-phosphate. 相似文献
7.
Rate constants have been determined for hydrolysis of the acetate, glutarate, and phthalate monoesters of 2-hydroxy-1,10-phenanthroline in water at 30°C and μ = 0.1 M with KCl. The hydrolysis reactions of the esters are hydroxide ion catalyzed at pH > 9. The phthalate and glutarate monoesters have in addition pH-independent reactions from pH 5.5 to 9 that involve intramolecular participation by the neighboring carboxylate anion. The pH-independent reaction of the glutarate monoester is 5-fold faster than that of the phthalate monoester. The plots of log kobsd vs pH for hydrolysis of the carboxyl substituted esters are bell shaped at pH < 5, which indicates a rapid reaction of the zwitterionic species (carboxyl anion and protonated phenanthroline nitrogen). The divalent metal ions, Cu2+, Ni2+, Zn2+, and Co2+, complex strongly with the esters; saturation occurs at metal ion concentrations less than 0.01 M. The 1:1 metal ion complexes have greatly enhanced rates of hydrolysis; the second-order rate constants for the OH− reactions are increased by factors of 105 to 108 by the metal ion. The pH-rate constant profiles for the phthalate and glutarate ester metal ion complexes have a sigmoidal region below pH 6 that can be attributed to a metal ion-promoted carboxylate anion nucleophilic reaction. The carboxyl group reactions are enhanced 102 - to 103 -fold by the metal ions, which allows the neighboring group reaction to be competitive with the favorable metal ion-promoted OH− reaction at pH < 6, but not at pH > 6. The half-lives of the pH-independent neighboring carboxyl group reactions of the Cu(II) complexes at 30°C are l2 s. The other metal ion complexes are only slightly less reactive (half-lives vary from 2.5 to 40 s). These are the most rapid neighboring carboxyl group reactions that have been observed in ester hydrolysis. 相似文献
8.
Mohamed Guerfali Ines Maalej Ali Gargouri Hafedh Belghith 《Journal of Molecular Catalysis .B, Enzymatic》2009,57(1-4):242-249
The present study explores the efficiency of Talaromyces thermophilus β-xylosidase, in the production of xylose and xylooligosaccharides. The β-xylosidase was immobilized by different methods namely ionic binding, entrapment and covalent coupling and using various carriers. Chitosan, pre-treated with glutaraldehyde, was selected as the best support material for β-xylosidase immobilization; it gave the highest immobilization and activity yields (94%, 87%, respectively) of initial activity, and also provided the highest stability, retaining 94% of its initial activity even after being recycled 25 times. Shifts in the optimal temperature and pH were observed for the immobilized β-xylosidase when compared to the free enzyme. The maximal activity obtained for the immobilized enzyme was achieved at pH 8.0 and 53 °C, whereas that for the free enzyme was obtained at pH 7.0 and 50 °C. The immobilized enzyme was more thermostable than the free β-xylosidase. We observed an increase of the Km values of the free enzyme from 2.37 to 3.42 mM at the immobilized state. Native and immobilized β-xylosidase were found to be stimulated by Ca2+, Mn2+ and Co2+ and to be inhibited by Zn2+, Cu2+, Hg2+, Fe2+, EDTA and SDS. Immobilized enzyme was found to catalyze the reverse hydrolysis reaction, forming xylooligosaccharides in the presence of a high concentration of xylose. In order to examine the synergistic action of xylanase and β-xylosidase of T. thermophilus, these two enzymes were co-immobilized on chitosan. A continuous hydrolysis of 3% Oat spelt xylan at 50 °C was performed and better hydrolysis yields and higher amount of xylose was obtained. 相似文献
9.
《BBA》1987,893(2):275-288
The membrane-bound ATP synthase from chloroplasts can occur in different redox and activation states. In the absence of reductants the enzyme usually is oxidized and inactive, Eoxi. Illumination in the presence of dithiothreitol leads to an active, reduced enzyme, Ereda. If this form is stored in the dark in the presence of dithiothreitol an inactive, reduced enzyme Eredi is formed. The rates of ATP synthesis and ATP hydrolysis catalyzed by the different enzyme species are measured as a function of ΔpH (Δψ = 0 mV). The ΔpH was generated with an acid-base transition using a rapid-mixing quenched flow apparatus. The following results were obtained. (1) The oxidized ATP synthase catalyzes high rates of ATP synthesis, voxmax = 400 ATP per CF0F1 per s. The half-maximal rate is obtained at ΔpH = 3.4. (2) The active, reduced ATP synthase catalyzes high rates of ATP synthesis, vredmax = 400 ATP per CF0F1 per s. The half-maximal rate is obtained at ΔpH = 2.7. It catalyzes also high rates of ATP hydrolysis vredmax = −90 ATP per CF0F per s at ΔpH = 0. (3) The inactive species (both oxidized and reduced) catalyze neither ATP synthesis nor ATP hydrolysis. The activation/inactivation of the reduced enzyme is completely reversible. (4) The activation of the reduced, inactive enzyme is measured as a function of ΔpH by measuring the rate of ATP hydrolysis catalyzed by the active species. Half-maximal activation is observed at ΔpH = 2.2. (5) On the basis of these results a reaction scheme is proposed relating the redox reaction, the activation and the catalytic reaction of the chloroplast ATP synthase. 相似文献
10.
《Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism》1992,1123(2):163-169
The effect of various detergents on polyphosphoinositide-specific phospholipase C activity in highly purified wheat root plasma membrane vesicles was examined. The plasma membrane-bound enzyme was solubilized in octylglucoside and purified 25-fold by hydroxylapatite and ion-exchange chromatography. The purified enzyme catalyzed the hydrolysis of phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) with specific activities of 5 and 10 μmol/min per mg protein, respectively. Phosphatidylinositol (PI) was not a substrate. Optimum activity was between pH 6–7 (PIP) and pH 6–6.5 (PIP2). The enzyme was dependent on micromolar concentrations of Ca2+ for activity, and millimolar Mg2+ further increased the activity. Other divalent cations (4 mM Ca2+, Mn2+ and Co2+) inhibited (PIP2 as substrate) or enhanced (PIP as substrate) phospholipase C activity. 相似文献
11.
The hen oviduct shell gland is a highly active calcium-transporting epithelial tissue which is responsible for the mineralization of the egg shell. We have identified a calcium-stimulated ATPase present at high specific activity in membrane preparations from shell gland mucosal shavings. In the presence of optimal MgCl2 (5 mm) and a Ca2+ buffer, ATP hydrolysis was stimulated by addition of low concentrations of free Ca2+ (K0.5 ~0.4 μm); but not by similar concentrations of Mn2+, Zn2+, Co2+, or La2+. This stimulation was specific for ATP; there was little or no effect of Ca2+ on hydrolysis of ADP, AMP, GTP, ITP, or p-nitrophenyl phosphate. Calcium-stimulated ATPase activity was inhibited by chlorpromazine, trifluoperazine, and quercetin, as well as by sulfhydryl-blocking agents, but not by oligomycin or ouabain. No significant effect of calmodulin was observed. Finally, low concentrations of free Ca2+ (10 to 100 μm) in the presence or absence of Mg2+ stimulated transfer of 32P from [γ-32P]ATP to a 105,000 molecular weight shell gland membrane protein. This phosphoprotein was sensitive to hydrolysis by heating or by hydroxylamine treatment at acidic pH, and its formation was not inhibited by addition of K+. The specific activity of Ca2+-ATPase in total membrane preparations from laying hen shell gland ranged from 80 to 150 nmol/min/ mg protein, similar to or greater than levels found in purified plasma membrane fractions from a variety of tissues. No significant activity was found in membrane preparations from the magnum or isthmus regions of the oviduct, which are not involved in egg shell calcification. The characteristics of the Ca2+-ATPase, its high specific activity, and its preferential localization in the shell gland region of the oviduct suggest a role for an ATP-dependent calcium transport system in egg shell mineralization. 相似文献
12.
R. L. Barchi 《Journal of neurochemistry》1976,26(4):715-720
—The hydrolysis of ThTP by rat brain membrane-bound ThTPase is inhibited by nucleoside diphosphates and triphosphates. ATP and ADP are most effective, reducing hydrolysis by 50% at concentrations of 2 × 10?5m and 7·5 × 10?5m respectively. Nucleoside monophosphates and free nuclcosides as well as Pi have no effect on enzyme activity. ThMP and ThDP also fail to inhibit hydrolysis in concentrations up to 5 × 10?3m . Non-hydrolysable methylene phosphate analogs of ATP and ADP were used in further kinetic studies with the ThTPase. The mechanism of inhibition by these analogs is shown to be of mixed non-competitive nature for both compounds. An observed Ki, of 4 × 10?5m for the ATP analog adenosine-PPCP and 9 × 10?5m for the ADP analog adenosine-PCP is calculated at pH 6·5. Formation of the true enzyme substrate, the [Mg2+. ThTP] complex, is not significantly affected by concentrations of analogs producing maximal (>95%) inhibition of enzyme activity. Likewise the relationships between pH and observed Km and pH and Vmax are not shifted by the presence of similar concentrations of inhibitor. 相似文献
13.
The hydrolytic activity of chromatophore membrane-bound pyrophosphatase with Zn-PPi2− as substrate was studied and compared with Mg-PPi2− hydrolysis. The pH profile of Zn-PPi2− hydrolysis is a bell shaped curve with an optimum at 5.25. This behavior is different from the sigmoidal profile obtained for Mg-PPi2− hydrolysis, which has a plateau from pH 6.5 to 9.0. Zn-PPi2− hydrolytic activity is inhibited by 1-butanol and methylene-diphosphate but not by NaF. The enzyme has no activity when free Zn2+ concentration is lower than 7.5 pM (at 0.9–1.2 mm Zn-PPi2− and therefore free Zn2+ is an essential activator of Zn-PPi2− hydrolytic activity. Free Mg2+, on the contrary, acts as an inhibitor of Zn-PPi2− hydrolysis. The dependence of the reaction rate on the Zn-PPi2− concentration is sigmoidal. 相似文献
14.
Gethyn J. Allen Francisco Morais Shelagh Muir R. Gareth Wyn Jones Roger A. Leigh 《Physiologia plantarum》1995,94(3):506-514
Microsomal fractions from wheat tissues exhibit a higher level of ATP hydrolytic activity in the presence of Ca2+ than Mg2+. Here we characterise the Ca2+-dependent activity from roots of Triticum aestivum lev. Troy) and investigate its possible function. Ca2+-dependent ATP hydrolysis in the microsomal fraction occurs over a wide pH range with two slight optima at pH 5.5 and 7.5. At these pHs the activity co-migrates with the major peak of nitrate-inhibited Mg2+. Cl-ATPase on continuous sucrose gradients indicating that it is associated with the vacuolar membrane. Ca2+-dependent ATP hydrolysis can be distinguished from an inhibitory effect of Ca2+ on the plasma membrane K+, Mg2+-ATPase following microsomal membrane separation using aqueous polymer two phase partitioning. The Ca2+-dependent activity is stimulated by free Ca2+ with a Km of 8.1 μM in the absence of Mg2+ ([CaATP] = 0.8 mM). Vacuoiar membrane vacuolar preparations contain a higher Ca2+-dependent than Mg2+-dependent ATP hydrolysis, although the two activities are not directly additive. The nucleotide specificity of the divalent ion-dependent activities in vacuolar membrane-enriched fractions was low. hydrolysis of CTP and UTP being greater than ATP hydrolysis with both Ca2+ and Mg2+ The Ca2+-dependent activity did discriminate against dinucleotides, and mononucleotides. and failed to hydrolyse phosphatase substrates. Despite low nucleotide specificity the Mg2+-dependent activity functioned as a bafilomycin sensitive H+-pump in vacuolar membrane vesicles. Ca2+-dependent ATP hydrolysis was not inhibited by the V-, P-, or F-type ATPase inhibitors bafilomycin. vanadate and azide, respectively. nor by the phosphatase inhibitor molybdate, but was inhibited 20% at pH 7.5 by K+. Possible functions of Ca2+-dependent hydrolysis as a H+-pump or a Ca2+-pump was investigated using vacuolar membrane vesicles. No H+ or Ca2+ translocating activity was observed under conditions when the Ca2+-dependent ATP hydrolysis was active. 相似文献
15.
Characterization of the Effects of Divalent Cations on the Coupled Activities of the H-ATPase in Tonoplast Vesicles 总被引:4,自引:2,他引:2
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The substrate requirement of the H+-ATPase in purified corn root tonoplast vesicles was investigated. The coupled activities, ATP hydrolysis and proton pumping, were simultaneously supported only by Mg2+ or Mn2+. The presence of Ca2+ or Ba2+ did not significantly affect the coupled activities. The addition of Cd2+, Co2+, Cu2+, and Zn2+ inhibited both the hydrolysis of Mg-ATP and the proton transport. However, the inhibition of proton pumping was more pronounced. Based on equilibrium analysis, both ATP-complexed and free forms of these cations were inhibitory. Inhibition of the hydrolysis of Mg-ATP could be correlated to the concentrations of the ATP-complex of Zn. On the other hand, the free Cu2+ and Co2+ were effective in inhibiting hydrolysis. For proton pumping, the ATP complexes of Co2+, Cu2+, and Zn2+ were effective inhibitors. However, this inhibition could be further modulated by free Co2+, Cu2+, and Zn2+. While the equilibrium concentrations of Cd-ATP and free Cd2+ were not estimated, the total concentration of this cation needed to inhibit the coupled activities of the H+-ATPase was found to be in the range of 10 to 100 micromolars. The presence of free divalent cations also affected the structure of the lipid phase in tonoplast membrane as demonstrated by the changes of emission intensity and polarization of incorporated 1,6-diphenyl-1,3,5-hexatriene. The differential inhibition caused by these cations could be interpreted by interactions with the protogenic domain of the membrane as previously proposed in “indirect-link” mechanism. 相似文献
16.
Acid phosphatase purified from maize scutellum, upon acylation with succinic anhydride, still shows negative co-operativity for the hydrolysis of glucose-6-phosphate at pH 5.4. This phenomenon is abolished by glucose, for both native and succinylated enzymes, through stimulation of the initial velocities at sub-optimal substrate concentrations. However, negative co-operativity for the enzymatic hydrolysis of p-nitrophenylphosphate at pH 5.4 is suppressed only at high concentrations of glucose. Furthermore, the hydrolysis of p-nitrophenylphosphate is noncompetitively inhibited (low affinity form of the enzyme molecule) by glucose, which suggests the existence of different substrate binding sites. 相似文献
17.
Małgorzata Pleszczyńska Adrian Wiater Marcin Skowronek Janusz Szczodrak 《Preparative biochemistry & biotechnology》2013,43(4):335-347
Mutanases are enzymes that catalyze hydrolysis of α-1,3-glucosidic bonds in various α-glucans. One of such glucans, mutan, which is synthesized by cariogenic streptococci, is a major virulence factor for induction of dental caries. This means that mutan-degrading enzymes have potential in caries prophylaxis. In this study, we report the purification, characterization, and partial amino acid sequence of extracellular mutanase produced by the MP-1 strain of Paenibacillus curdlanolyticus, bacterium isolated from soil. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the purified enzyme showed a single protein band of molecular mass 134 kD, while native gel filtration chromatography confirmed that the enzyme was a monomer of 142 kD. Mutanase showed a pH optimum in the range from pH 5.5 to 6.5 and a temperature optimum around 40–45°C. It was thermostable up to 45°C, and retained 50% activity after 1 hr at 50°C. The enzyme was fully stable at a pH range of 4 to 10. The enzyme activity was stimulated by the addition of Tween 20, Tween 80, and Ca2+, but it was significantly inhibited by Hg2+, Ag+, and Fe2+, and also by p-chloromercuribenzoate, iodoacetamide, and ethylenediamine tetraacetic acid (EDTA). Mutanase preparation preferentially catalyzed the hydrolysis of various streptococcal mutans and fungal α-1,3-glucans. It also showed binding activity to insoluble α-1,3-glucans. The N-terminal amino acid sequence was NH2-Ala-Gly-Gly-Thr-Asn-Leu-Ala-Leu-Gly-Lys-Asn-Val-Thr-Ala-Ser-Gly-Gln. This sequence indicated an analogy of the enzyme to α-1,3-glucanases from other Paenibacillus and Bacillus species. 相似文献
18.
Iqbal Ahmad Zubair Anwar Kefi Iqbal Syed Abid Ali Tania Mirza Adeela Khurshid Aqeela Khurshid Adeel Arsalan 《AAPS PharmSciTech》2014,15(3):550-559
The photolysis of riboflavin (RF) in the presence of acetate buffer (pH 3.8–5.6) and carbonate buffer (pH 9.2–10.8) has been studied using a multicomponent spectrophotometric method for the simultaneous assay of RF and its photoproducts. Acetate and carbonate buffers have been found to catalyze the photolysis reaction of RF. The apparent first-order rate constants for the acetate-catalyzed reaction range from 0.20 to 2.86 × 10−4 s−1 and for the carbonate-catalyzed reaction from 3.33 to 15.89 × 10−4 s−1. The second-order rate constants for the interaction of RF with the acetate and the carbonate ions range from 2.04 to 4.33 × 10−4 M−1 s−1 and from 3.71 to 11.80 × 10−4 M−1 s−1, respectively. The k-pH profile for the acetate-catalyzed reaction is bell shaped and for the carbonate-catalyzed reaction a steep curve. Both HCO3− and CO32 − ions are involved in the catalysis of the photolysis reaction in alkaline solution. The rate constants for the HCO3− and CO32 − ions catalyzed reactions are 0.72 and 1.38 × 10−3 M−1 s−1, respectively, indicating a major role of CO32 − ions in the catalysis reaction. The loss of RF fluorescence in acetate buffer suggests an interaction between RF and acetate ions to promote the photolysis reaction. The optimum stability of RF solutions is observed in the pH range 5–6, which is suitable for pharmaceutical preparations.KEY WORDS: acetate effect, carbonate effect, photolysis, riboflavin, spectrophotometric assay 相似文献
19.
Between pH 7 and pH 10.5, p-nitrophenyl -sulfamyl benzoate (PNP-SAB) binds very strongly to human carbonic anhydrase B (dissociation constant on the order of 10?9 M or less at pH 7.5), but is not hydrolyzed by the enzyme. Because the binding is essentially stoichiometric under readily accessible conditions, this ester may be used as an active site titrant, by measuring the rapid hydrolysis of excess unbound PNP-SAB catalyzed by an added nucleophile (“reverse burst”). 相似文献
20.
Tzong-Shin Lin P.E. Kolattukudy 《Biochemical and biophysical research communications》1977,75(1):87-93
Treatment of cutinase, an extracellular glycoprotein produced by Fusarium solani f. pisi, with NaB3H4 at pH 7.0 generated labeled enzyme. Acid hydrolysis showed that all of the label was in an acidic carbohydrate which was identified as gulonic acid. The N-terminal amino group of the enzyme is blocked; the precursor of gulonic acid has a free reducing group and it is attached via a linkage resistant to β-elimination. Furthermore, pronase digestion of NaB3H4-treated cutinase gave rise to a ninhydrin negative compound which contained the bulk of the 3H and this compound was identified as N-gulonyl glycine. These results strongly suggest that the amino group of glycine, the N-terminal amino acid of this enzyme, is in amide linkage with glucuronic acid. 相似文献