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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Histidine ammonia-lyase (EC 4.3.1.3) activity in the cell-free extracts of Hartmannella culbertsoni has been partially purified and the optimum activity is found at pH 9.0--9.2. 2. The enzyme required sulphydryl groups for its activity. L-2-Thiohistidine and EDTA competitively inhibit the enzyme. 3. Its molecular weight, as determined by gel filtration technique, is 131,800 daltons and the energy of activation for this enzyme is 15,205 cals/mole. 4. Certain amoebicidal drug and divalent cations have marked inhibitory effect on the enzyme. Co2+ has a profound stimulatory effect.
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PMID:L-Histidine ammonia-lyase activity of axenically grown Hartmannella culbertsoni. 3 48

Homogeneous preparations of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase [7-phospho-2-keto-3-deoxy-D-arabino-heptonate D-erythrose-4-phosphate lyase (pyruvate phosphorylating), EC 4.1.2.15] isolated as the enzyme-phosphoenolpyruvate complex from Escherichia coli are shown by atomic absorption analysis to contain approximately one mole of iron per mole of native enzyme. No cobalt was found, in contrast to suggestions of earlier workers. Pure enzyme preparations show a unique absorption maximum around 350 nm with an epsilon value of about 3500 M-1cm-1. The 350-nm band as well as the enzyme activity is lost when the enzyme is denatured with guanidine-hydrochloride, or when phosphoenolpyruvate, the first substrate to bind to the enzyme, is totally removed from the enzyme by incubation with an excess of erythrose 4-phosphate, the second substrate to bind to the enzyme. The iron remains bound to the enzyme when phosphoenolpyruvate is removed from the enzyme-phosphoenolpyruvate complex.
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PMID:Iron, an essential element for biosynthesis of aromatic compounds. 3 83

The guanylate cyclase activity of axoneme--basal apparatus complexes isolated from bovine retinal rods has been investigated. The Mg2+ and Mn2+ complexes of GTP4- serve as substrates. Binding of an additional mole of Mg2+ or Mn2+ per mole of enzyme is required. Among cations which are ineffective are Ca2+, Ni2+, Fe2+, Fe3+, Zn2+, and Co2+. The kinetics are consistent with a mechanism in which binding of Mg2+ or Mn2+ to the enzyme must precede binding of MgGTP or MnGTP. The apparent dissociation constants of the Mg--enzyme complex and the Mn--enzyme complex are 9.5 x 10(-4) and 1.1 x 10(-4) M, respectively. The apparent dissociation constants for binding of MgGTP and MnGTP to the complex of the enzyme with the same metal are 7.9 x 10(-4) and 1.4 x 10(-4) M, respectively. The cyclase activity is maximal and independent of pH between pH 7 and 9. KCl and NaCl are stimulatory, especially at suboptimal concentrations of Mg2+ or Mn2+. Ca2+ and high concentrations of Mg2+ and Mn2+ are inhibitory. Ca2+ inhibition appears to require the binding of 2 mol of Ca2+ per mol of enzyme. The dissociation constant of the Ca2--enzyme complex is estimated to be 1.4 x 10(-6) M2. The axoneme--basal apparatus preparations contain adenylate cyclase activity whose magnitude is 1--10% that of the guanylate cyclase activity.
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PMID:Guanylate cyclase of isolated bovine retinal rod axonemes. 4 May 95

Two of 63 isolates from different sources were very active in producing thermostable aminopeptidase. Comparing the two isolates, RR-2247 gave the highest enzyme activity and was identified as Bacillus stearothermophilus. The enzyme was isolated from the cells by a sonic vibration for 3 minutes at 20 KC/S. The enzyme shows optimum activity over the pH range of 7.5-8.0 at 65 degrees C. The apparent temperature optimum was about 70 degrees C. Addition of 0.0001 M Co2+ ions stabilized the enzyme in solution for 60 minutes at 80 degrees C. The heat of the reaction (delta E) was calculated to be +10,600 cal/mole. The standard entropy change (delta S) and the standard free energy change (delta G) were + 22.9 cal/mole/degree and -341 cal/mole at 50 degrees C. Amino acids composition and infra-red spectrum of the enzyme were also studied.
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PMID:Thermostable aminopeptidase from local isolate of Bacillus stearothermophilus. 4 75

D-Ribulose-1,5-bisphosphate (RuBP) carboxylase has been purified from glutamate-CO2-S2O3(2)-grown Thiobacillus intermedius by pelleting the enzyme from the high-speed supernatant and by intermediary crystallization followed by sedimentation into a discontinuous 0.2 to 0.8 M sucrose gradient. The enzyme was homogeneous by the criteria of electrophoresis on polyacrylamide gels of several acrylamide concentrations, sedimentation velocity and equilibrium measurements, and electron microscopic observations of negatively stained preparations. The molecular weights of the enzyme determined by sedimentation equilibrium and light-scattering measurements averaged 462,500 +/- 13,000. The enzyme consisted of closely similar or identical polypeptide chains of a molecular weight of 54,500 +/- 5,450 determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The S(0)20,w of the enzyme was 18.07S +/- 0.22. Electron microscopic examination suggested that the octomeric enzyme (inferred from the molecular measurements mentioned) had a cubical structure. The specific activity of the enzyme was 2.76 mumol of RuBP-dependent CO2 fixed/min per mg of protein (at pH 8 and 30 C), and the turnover number in terms of moles of CO2 fixed per mole of catalytic site per second was 2.6. The enzyme was stable for 3 months at -20 C and at least 4 weeks at 0 C. The apparent Km for CO2 was 0.75 mM, and Km values for RuBP and Mg2+ were 0.076 and 3.6 mM, respectively. Dialyzed enzyme could be fully reactivated by the addition of 20 mM Mg2+ and partially reactivated by 20 mM Co2+, but Cd2+, Mn2+, Ca2+, and Zn2+ had no effect. The compound 6-phosphogluconate was a linear competitive inhibitor with respect to RuBP when it had been preincubated with enzyme, Mg2+, and HCO3-.
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PMID:Purification, quaternary structure, composition, and properties of D-ribulose-1,5-bisphosphate carboxylase from Thiobacillus intermedius. 81 23

Human carboxypeptidase A has been isolated from activated pancreatic juice by means of affinity chromatography employing the competitive inhibitor benzylsuccinic acid as an affinity ligand. The structural and functional features of the human and bovine enzymes are quite analogous. The molecular weights of human and bovine carboxypeptidases A are virtually identical, their amino acid compositions are similar, both contain 1 g-atom of zinc/mole, and the activities of both are restored by addition of zinc to the apoenzyme. The inhibition of human carboxypeptidase by chelating agent is reversed by either dilution or addition of a metal such as Cu2+. When other metals are substituted for the native zinc, peptidase activity of the human metallocarboxypeptidases follows the order: cobalt greater than nickel greater than manganese greater than cadmium, while the sequence for esterase activities is: manganese greater than cobalt = cadmium greater than nickel. The latter sequence differs from that observed for the bovine enzyme. Human carboxypeptidase A crystallizes after dialysis at low ionic strength. Hydrolysis of the dipeptide carbobenzoxyglycyl-L-phenylalanine and of the ester benzoylglycyl-L-alpha-hydroxy-beta-phenyllactate exhibits kinetic anomalies, but that of their longer homologues does not. Chemical modifications with tyrosine reagents alters esterase and peptidase activities. The affinity chromatographic method here described should greatly facilitate future studies of this enzyme from human and other sources.
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PMID:Purification and crystallization of human carboxypeptidase A. 93 22

Alkaline phosphatase of E. coli, isolated by procedures which do not alter its intrinsic metal content, contains 1.3 +/- 0.3 g-atom of magnesium and 4.0 +/- 0.2 g-atom of zinc per molecule of molecular weight 89,000. Magnesium, the role of which has been unappreciated, significantly affects the function and structure of alkaline phosphatase containing either 2 or 4 g-atom of zinc per mole. Magnesium does not activate the apoenzyme but increases the activity of the enzyme containing 2 g-atom of zinc 4.4-fold and that of the enzyme containing 4 g-atom 1.2-fold. The results obtained with enzyme in which cobalt is substituted for zinc are analogous. Moreover, the absorption and electron paramagnetic resonance spectra of cobalt phosphatases reveal the effects of magnesium on cobalt coordination geometry. Addition of magnesium changes the spectral characteristics of the apoenzyme reconstituted with 2 g-atom of cobalt from predominantly octahedral to 4- or 5-coordinate geometry. These two classes of cobalt binding sites have been associated with catalysis and structure stabilization, respectively. Therefore, magnesium controls the occupancy of the catalytic and structural binding sites and modulates the resultant enzymatic activity. Hydrogen-tritium exchange was employed to determine the effects of magnesium on the conformational stability of phosphatase. Magnesium stabilizes the dynamic structural properties, both of apophosphatase and of enzyme containing 2 g-atom of zinc, which is further stabilized by 2 more zinc atoms. The role of magnesium and other metal ions in regulatory processes, only now beginning to be explored fully, will likely emerge as an important avenue for achievement of regulatory effects in metalloenzymes.
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PMID:Role of magnesium in Escherichia coli alkaline phosphatase. 110 31

The effect of electrostatically binding ferrous cytochrome c to anionic liposomes, composed of dimyristoyl phosphatidylglycerol (DMPG-), dioleoyl phosphatidyl-glycerol (DOPG-), or cardiolipin (CL2-) mixed with varying amounts of egg phosphatidylcholine (PC), on the kinetics of cytochrome oxidation by the positively charged cobalt phenanthroline ion has been measured using stopped-flow spectrophotometry. The rate of electron transfer is enhanced as much as 3000-fold by increasing the number of negatively charged binding sites on the liposome surface, and by as much as 1000-fold by decreasing the ionic strength of the buffer. The sigmoidal shape of the curve of rate constant vs mole percent anionic lipid is consistent with a positively cooperative effect of the negative surface charge. The rate stimulation is greater for DOPG(-)- and CL2(-)-containing liposomes than for DMPG- vesicles; this is most likely due to structural differences in the respective liposomes. The results do not provide any support for a role of structural changes in the bound cytochrome in influencing oxidation kinetics, a possibility suggested by recent spectroscopic measurements, although relatively small conformational effects cannot be completely ruled out.
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PMID:Electrostatic modulation of the kinetics of electron transfer from cytochrome c to cobalt phenanthroline by binding to lipid bilayers: effects of ionic strength and extent of incorporation of various negatively charged lipids. 131 3

The D-aminoacylase produced by Alcaligenes denitrificans DA181 was a new type of aminoacylase which had both high stereospecificity and specific activity. The molecular weight and isoelectric point of this enzyme were 58,000 and 4.4, respectively. The apparent Km and kcat values of this enzyme for N-acetyl-D-methionine were estimated to be 0.48 mM and 6.24 x 10(4) min-1, respectively. The optimum temperature was 45 degrees C. The enzyme was stable up to 55 degrees C for 1 hr in the presence of 0.2 mg/ml bovine serum albumin. The enzyme was stable in the pH range of 6.0 to 11.0 with an optimum pH of 7.5. This enzyme contained about 2.1 g atom of zinc per mole of enzyme. Enzyme activity was inhibited by incubation with EDTA. The inhibition by EDTA was fully reversed by Co2+ and partially by Zn2+.
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PMID:Characterization of D-aminoacylase from Alcaligenes denitrificans DA181. 136 43

The effect of binding reduced tuna mitochondrial cytochrome c to negatively charged lipid bilayer vesicles at low ionic strength on the kinetics of electron transfer to various oxidants was studied by stopped-flow spectrophotometry. Binding strongly stimulated (up to 100-fold) the rate of reaction with the positively charged cobalt phenanthroline ion, whereas the rate of reaction with the negatively charged ferricyanide ion was greatly inhibited (up to 60-fold), as compared with the same systems either at high ionic strength or at low ionic strength either in the presence of electrically neutral vesicles or in the absence of vesicles. Reactions of tuna cytochrome c with uncharged or electrically neutral oxidants such as benzoquinone and Rhodospirillum rubrum cytochrome c2 were unaffected by binding to vesicles, suggesting little or no effect of membrane association on cytochrome structure or accessibility of the heme center. The kinetic effects were largest at lower cytochrome c to vesicle ratios, where there was a greater degree of exposure of negatively charged regions on the membrane. The reduction of cobalt phenanthroline and ferricyanide by bound cytochrome c proceeded by nonexponential kinetics, as compared with the monophasic kinetics observed in the absence of vesicles. This was probably due to the heterogeneous distribution of vesicle sizes which exists at a given lipid to protein ratio. Nonlinear oxidant concentration dependencies were observed for cobalt phenanthroline oxidation of membrane-bound cytochrome c, consistent with a (minimal) two-step kinetic mechanism involving association of the oxidant with the membrane followed by electron transfer. Based on a comparison of second-order rate constants as a function of lipid to protein mole ratio, binding of cytochrome c to the bilayer increased the efficiency of the cobalt phenanthroline reaction by a factor of approximately 500 at the highest lipid:protein ratio used. The results suggest a mechanism involving attractive and repulsive electrostatic interactions between the negatively charged bilayer and the electrically charged oxidants, which increase or decrease their effective concentrations at the membrane surface.
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PMID:Electrostatic effects on the kinetics of electron transfer reactions of cytochrome c caused by binding to negatively charged lipid bilayer vesicles. 165 79


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