Large hydrophobic interactions with clearly defined geometry. A dimeric steroid with catalytic properties

1982 ◽  
Vol 60 (6) ◽  
pp. 747-764 ◽  
Author(s):  
J. Peter Guthrie ◽  
Patricia A. Cullimore ◽  
Robert S. McDonald ◽  
Stella O'Leary
Keyword(s):  
Design Parameter ◽  
Reductive Amination ◽  
Catalytic Properties ◽  
Hydrophobic Interactions ◽  
Artificial Enzymes ◽  
Sodium Cyanoborohydride ◽  
Rate Enhancement ◽  
Nitrobenzoic Acid ◽  
Transition State Geometry ◽  
Hydrolysis Of

The steroid dimer α,α′-bis(17β-(4'-imidazolyl)-11-keto-5α- androstan-3β-amino)-p-xylene, 3, has been synthesized by reductive animation of 17β-(4′-imidazolyl)-5α- androstane-3,11-dione by p-xylenediamine in the presence of sodium cyanoborohydride, and by reductive amination of terephthalaidehyde by 3β-amino-17β-(4′-imidazolyl)-5α- androstan-11-one. The second method is stereochemically unambiguous; the first is not. Compound 3 acts as a catalyst for the hydrolysis of 3-arylpropionate esters of 3-hydroxy-4-nitrobenzoic acid. For the phenanthryl propionate the rate enhancement relative to imidazole is 200-fold, and the rate enhancement relative to the hypothetical rate for the propionate reacting with the steroid by the same transition state geometry is 3000-fold. The slope of a plot of log kcorr vs. π for the reaction of 3b with aryl propionate esters was 0.83; the corresponding slope for 12 was 0.39. This provides a design parameter for the construction of artificial enzymes.

Water Soluble Steroids with Catalytic Substituents II. Synthesis of 3β-(4(5)-Imidazolyl)-5α-androstane-11β, 17β,-diamine and Comparison of its Catalytic Properties with Those of 17β-(4(5)-Imidazolyl)-5α-androstane-3β, 11β-diamine

1973 ◽  
Vol 51 (23) ◽  
pp. 3936-3942 ◽  
Author(s):  
J. Peter Guthrie ◽  
Yasutsugu Ueda
Keyword(s):  
Catalytic Properties ◽  
Lead Tetraacetate ◽  
Water Soluble ◽  
Keto Group ◽  
Rate Enhancement ◽  
Multistep Process ◽  
Acid Catalyzed ◽  
Hydrolysis Of

3β-(4(5)-Imidazolyl)-5α-androstane-11β,17β-diamine, 15, has been synthesized in a multistep process from adrenosterone, 2, starting with lithium ammonia reduction to give 11α,17β-dihydroxy-5α-androstan-3-one, 3, which was converted to its diacetate, 4. Ethynylation at the 3 keto group gave the ethynyl triol 5, purified as its11,17-diacetate 6. Acid catalyzed rearrangement of 6 gave 3-acetyl-5α-androst-2-ene-11α,17β-diol diacetate, 7. This was hydrogenated, and then subjected to base catalyzed hydrolysis and equilibration to give crystalline 3β-acetyl-5α-androstane-11α,17β-diol, 9, which was converted to 3β-acetoxyacetyl-5α-androstane-11α,17β-diol, 10, using lead tetraacetate. After hydrolysis to the triol, 11, the Weidenhagen reaction led to formation of 3β-imidazolyl-5α-androstane-11α,17β-diol, 12. Finally oxidation to the dione, 13, formation of the dioxime, 14, and hydrogénation give 15. As expected 15 is a better catalyst than 17β-(4(5)-imidazolyl-5α-androstane-3β,11β-diamine, 1, for the hydrolysis of aryl esters of acids with hydrophobic substituents, but the effect is small. With 1 there is a marked electrostatic rate enhancement or retardation when charged groups are present on the aryl esters; this effect is much smaller for 15.

On the Preparation of Bovine α-Thrombin

1978 ◽  
Vol 39 (01) ◽  
pp. 193-200 ◽  
Author(s):  
Erwin F Workman ◽  
Roger L Lundblad
Keyword(s):  
Immobilized Enzyme ◽  
Catalytic Properties ◽  
Specific Activity ◽  
Guanidine Hydrochloride ◽  
Low Molecular Weight ◽  
Reversible Process ◽  
Gel Beads ◽  
Tissue Thromboplastin ◽  
C 50 ◽  
Hydrolysis Of

SummaryAn improved method for the preparation of bovine α-thrombin is described. The procedure involves the activation of partially purified prothrombin with tissue thromboplastin followed by chromatography on Sulfopropyl-Sephadex C-50. The purified enzyme is homogeneous on polyacrylamide discontinuous gel electrophoresis and has a specific activity toward fibrinogen of 2,200–2,700 N.I.H. U/mg. Its stability on storage in liquid media is dependent on both ionic strenght and temperature. Increasing ionic strength and decreasing temperature result in optimal stability. The denaturation of α-thrombin by guanidine hydrochloride was found to be a partially reversible process with the renatured species possessing properties similar to “aged” thrombin. In addition, the catalytic properties of a-thrombin covalently attached to agarose gel beads were also examined. The activity of the immobilized enzyme toward fibrinogen was affected to a much greater extent than was the hydrolysis of low molecular weight, synthetic substrates.

The effect of polymeric and model imidazolium halides on the rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid

1985 ◽  
Vol 50 (4) ◽  
pp. 845-853 ◽  
Author(s):  
Miloslav Šorm ◽  
Miloslav Procházka ◽  
Jaroslav Kálal
Keyword(s):  
Catalyst Concentration ◽  
Low Molecular Weight ◽  
Imidazolium Chloride ◽  
First Order ◽  
Nitrobenzoic Acid ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Ethanol In Water ◽  
Direct Attack

The course of hydrolysis of an ester, 4-acetoxy-3-nitrobenzoic acid catalyzed with poly(1-methyl-3-allylimidazolium bromide) (IIa), poly[l-methyl-3-(2-propinyl)imidazolium chloride] (IIb) and poly[l-methyl-3-(2-methacryloyloxyethyl)imidazolium bromide] (IIc) in a 28.5% aqueous ethanol was investigated as a function of pH and compared with low-molecular weight models, viz., l-methyl-3-alkylimidazolium bromides (the alkyl group being methyl, propyl, and hexyl, resp). Polymers IIb, IIc possessed a higher activity at pH above 9, while the models were more active at a lower pH with a maximum at pH 7.67. The catalytic activity at the higher pH is attributed to an attack by the OH- group, while at the lower pH it is assigned to a direct attack of water on the substrate. The rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid is proportional to the catalyst concentration [IIc] and proceeds as a first-order reaction. The hydrolysis depends on the composition of the solvent and was highest at 28.5% (vol.) of ethanol in water. The hydrolysis of a neutral ester, 4-nitrophenyl acetate, was not accelerated by IIc.

scholarly journals PHYSICAL CHEMICAL STUDIES OF THE SURFACTANT DILAURYLDIMETHYLAMMONIUM BROMIDE (DLDMAB): AGGREGATION AND CATALYTIC PROPERTIES

2009 ◽  
Vol 17 (17) ◽  
pp. 21-32
Author(s):  
Elizabeth Fatima de Souza ◽  
Silvia Dani ◽  
Lavinel G. IONESCU
Keyword(s):  
Thermodynamic Parameters ◽  
Catalytic Properties ◽  
Activation Parameters ◽  
Critical Micellar Concentration ◽  
Physical Chemical ◽  
Chemical Studies ◽  
Diphenyl Phosphate ◽  
C 32 ◽  
Free Energy Of Micellization ◽  
Hydrolysis Of

The micellization of dilauryldimethylammonium bromide (DLDMAB) in water was studied by using surface tension measurements. The critical micellar concentration (CMC) was determined at 25°C, 32°C and 40°C and thermodynamic parameters such as the free energy of micellization (∆G°mic), enthalpy (∆H°mic), and entropy (∆S°mic) of micellization were measured. The CMC at 25°C was 4.93 x 10-5 M and the corresponding values of the thermodynamic parameters were: ∆G°mic = -5.87 kcal/mol; ∆H°mic = -1.12 kcal/mol and ∆S°mic = +16.00 e.u. Micelles of the surfactant DLDMAB act as catalysts for the alkaline hydrolysis of p-nitrophenyl diphenyl phosphate (NPDPP) with a maximum catalytic factor of approximately 120 compared to 80 for CTAB. Typical activation parameters measured for 1.00 x 10-3 M surfactant and 0.005 M NaOH were: Ea = 9.7 kcal/mo/; ∆H°≠ = 9.1 kcal/mol; ∆G°≠ = 19.6 kcal/mol and ∆S°≠ = -33.9 e.u. The kinetic results were also analyzed in terms of the pseudo-phase ion-exchange models (PPIE) and showed that the model is applicable to describe the experimental results.

scholarly journals Peptidase activity of β-lactamases

1999 ◽  
Vol 341 (2) ◽  
pp. 409-413 ◽  
Author(s):  
Noureddine RHAZI ◽  
Moreno GALLENI ◽  
Michael I. PAGE ◽  
Jean-Marie FRÈRE
Keyword(s):  
Molecular Mass ◽  
Enterobacter Cloacae ◽  
Peptidase Activity ◽  
Rate Enhancement ◽  
Enhancement Factors ◽  
Lactam Ring ◽  
Class C ◽  
Hydrolysis Of

Although β-lactamases have generally been considered as being devoid of peptidase activity, a low but significant hydrolysis of various N-acylated dipeptides was observed with representatives of each class of β-lactamases. The kcat/Km values were below 0.1 M-1˙s-1, but the enzyme rate enhancement factors were in the range 5000-20000 for the best substrates. Not unexpectedly, the best ‘peptidase’ was the class C β-lactamase of Enterobacter cloacae P99, but, more surprisingly, the activity was always higher with the phenylacetyl- and benzoyl-D-Ala-D-Ala dipeptides than with the diacetyl- and α-acetyl-L-Lys-D-Ala-D-Ala tripeptides, which are the preferred substrates of the low-molecular-mass, soluble DD-peptidases. A comparison between the β-lactamases and DD-peptidases showed that it might be as difficult for a DD-peptidase to open the β-lactam ring as it is for the β-lactamases to hydrolyse the peptides, an observation which can be explained by geometric and stereoelectronic considerations.

Hydrogen generation by hydrolysis of alkaline NaBH4 solution on Co–Mo–Pd–B amorphous catalyst with efficient catalytic properties

2012 ◽  
Vol 207 ◽  
pp. 120-126 ◽  
Author(s):  
Yanchun Zhao ◽  
Zhen Ning ◽  
Jianniao Tian ◽  
Huaiwen Wang ◽  
Xiaoyu Liang ◽  
...  
Keyword(s):  
Hydrogen Generation ◽  
Catalytic Properties ◽  
Hydrolysis Of

scholarly journals Active-site modification of native and mutant forms of inosine 5′-monophosphate dehydrogenase from Escherichia coli K12

1980 ◽  
Vol 191 (2) ◽  
pp. 533-541 ◽  
Author(s):  
Harry J. Gilbert ◽  
William T. Drabble
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Enzyme Inactivation ◽  
Enzyme Hydrolysis ◽  
Thiol Groups ◽  
Imp Dehydrogenase ◽  
Nitrobenzoic Acid ◽  
Saturation Kinetics ◽  
Mutant Forms ◽  
Hydrolysis Of

IMP dehydrogenase of Escherichia coli was irreversibly inactivated by Cl-IMP (6-chloro-9-β-d-ribofuranosylpurine 5′-phosphate, 6-chloropurine ribotide). The inactivation reaction showed saturation kinetics. 6-Chloropurine riboside did not inactivate the enzyme. Inactivation by Cl-IMP was retarded by ligands that bind at the IMP-binding site. Their effectiveness was IMP>XMP>GMP»AMP. NAD+ did not protect the enzyme from modification. Inactivation of IMP dehydrogenase was accompanied by a change in λmax. of Cl-IMP from 263 to 290nm, indicating formation of a 6-alkylmercaptopurine nucleotide. The spectrum of 6-chloropurine riboside was not changed by IMP dehydrogenase. With excess Cl-IMP the increase in A290 with time was first-order. Thus it appears that Cl-IMP reacts with only one species of thiol at the IMP-binding site of the enzyme: 2–3mol of Cl-IMP were bound per mol of IMP dehydrogenase tetramer. Of ten mutant enzymes from guaB strains, six reacted with Cl-IMP at a rate similar to that for the native enzyme. The interaction was retarded by IMP. None of the mutant enzymes reacted with 6-chloropurine riboside. 5,5′-Dithiobis-(2-nitrobenzoic acid), iodoacetate, iodoacetamide and methyl methanethiosulphonate also inactivated IMP dehydrogenase. Reduced glutathione re-activated the methanethiolated enzyme, and 2-mercaptoethanol re-activated the enzyme modified by Cl-IMP. IMP did not affect the rate of re-activation of methanethiolated enzyme. Protective modification indicates that Cl-IMP, methyl methanethiosulphonate and iodoacetamide react with the same thiol groups in the enzyme. This is also suggested by the low incorporation of iodo[14C]acetamide into Cl-IMP-modified enzyme. Hydrolysis of enzyme inactivated by iodo[14C]acetamide revealed radioactivity only in S-carboxymethylcysteine. The use of Cl-IMP as a probe for the IMP-binding site of enzymes from guaB mutants is discussed, together with the possible function of the essential thiol groups.

Kinetic properties of the α-lytic protease of Sorangium sp., a bacterial homologue of the pancreatopeptidases

1969 ◽  
Vol 47 (3) ◽  
pp. 305-316 ◽  
Author(s):  
H. Kaplan ◽  
D. R. Whitaker
Keyword(s):  
Methyl Ester ◽  
Catalytic Properties ◽  
Substrate Binding ◽  
Kinetic Properties ◽  
Histidine Residue ◽  
Amino Groups ◽  
Binding Properties ◽  
Histidine Residues ◽  
Support Reaction ◽  
Hydrolysis Of

The kinetics under consideration are those of a bacterial serine protease with the same "active serine" sequence as chymotrypsin, trypsin, and elastase, and with a single histidine residue in a sequence which closely matches the sequences around histidine-57 of chymotrypsin and the analogous histidine residues of trypsin and elastase. In agreement with previous evidence of an elastase-like specificity, esters of N-substituted, neutral, aliphatic L-amino acids proved to be good to excellent substrates for the α-enzyme; esters of arginine, tyrosine, and tryptophan were not hydrolyzed. The enzyme has a much higher activity than the pancreatopeptidases towards p-nitrophenyl acetate and p-nitrophenyl trimethyl acetate; the catalytic rate coefficient kc for the latter substrate is about fivefold greater than that of elastase.The catalytic properties match those of the pancreatopeptidases in the following respects. As demonstrated with N-acetyl-L-valine methyl ester as substrate, kc is dependent on an ionization with a pKa of 6.7 in water and 7.3 in H22O; Δ log (kc/Km)/ΔpH for this ionization is equal to 1.0; kc is reduced 50% when H2O is replaced by H22O. These findings are consistent with a requirement for a single unprotonated histidine residue and general basic catalysis by that residue. The burst of p-nitrophenol in hydrolyses of p-nitrophenyl trimethyl acetate is proportional to [E]0; the magnitude of the proportionality factor and the rate of attainment of a steady state are consistent with the condition [Formula: see text], as in chymotrypsin kinetics. Thus the purely catalytic properties of the α-enzyme match those of chymotrypsin very closely. These findings do not support reaction mechanisms which require two catalytically functional histidine residues for such catalysis. The substrate-binding properties of the α-enzyme differ from those of chymotrypsin in that substrate binding does not depend on ionization of an N-terminal α-amino group; Km for the hydrolysis of N-acetyl-L-valine methyl ester is constant from pH 5 to pH 10 and enzymatic activity is unaffected by acetylation of the enzyme's α- and ε-amino groups. Ks for the hydrolysis of p-nitrophenyl trimethyl acetate is appreciably greater than the Ks of elastase for this substrate.The chloromethyl ketones of glycine and valine did not inhibit the enzyme or alkylate its histidine residue.

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