Displaying publications 1 - 20 of 898 in total

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  1. Makar AB, McMartin KE, Palese M, Tephly TR
    Biochem Med, 1975 Jun;13(2):117-26.
    PMID: 1
    Matched MeSH terms: Kinetics
  2. Garner CW, Behal FJ
    Biochemistry, 1975 Nov 18;14(23):5084-8.
    PMID: 38
    The presence of at least two ionizable active center groups has been detected by a study of the effect of pH upon catalysis of hydrolysis of L-alanyl-beta-naphthylamide by human liver alanine aminopeptidase and upon the inhibition of hydrolysis by inhibitors and substrate analogs. Octanoic acid, octylamine, and peptide inhibitors have been found to be competitive inhibitors and are therefore thought to bind the active center. L-Phe was previously shown to bind the active center since it was found to be a competitive inhibitor of the hydrolysis of tripeptide substrates (Garner, C. W., and Behal, F. J. (1975), Biochemistry 14, 3208). A plot of pKm vs. pH for the substrate L-Ala-beta-naphthylamide showed that binding decreased below pH 5.9 and above 7.5, the points at which the theoretical curve undergoes an integral change in slope. These points are interpreted as the pKa either of substrate ionizable groups or binding-dependent enzyme active center groups. Similar plots of pKm vs. pH for L-alanyl-p-nitroanilide (as substrate) and pKi vs. pH for L-Leu-L-Leu-L-Leu and D-Leu-L-Tyr (as inhibitors) gave pairs fo pKa values of 5.8 and 7.4, 6.0 and 7.5, and 5.7 and 7.5, respectively. All the above substrates (and D-Leu-L-Tyr) have pKa values near 7.5; therefore, the binding-dependent group with a pKa value near 7.5 is possibly this substrate group. Similar plots of pKi vs. pH for the inhibitors L-Phe, L-Met, L-Leu, octylamine, and octanoic acid had only one bending point at 7.7, 7.6, 7.4, 6.3, and 5.9, respectively. Amino acid inhibitors, octylamine, and octanoic acid have no groups with pKa values between 5 and 9. These data indicate that there are two active center ionizable groups with pKa values of approximately 6.0 and 7.5 which are involved in substrate binding or inhibitory amino acid binding but not in catalysis since Vmax was constant at all pH values tested.
    Matched MeSH terms: Kinetics
  3. Johanson RA, Reeves HC
    Biochim. Biophys. Acta, 1977 Jul 08;483(1):24-34.
    PMID: 18195
    Oxalacetate and glyoxylate are each weak inhibitors of NADP+-specific isocitrate dehydrogenase (threo-DS-isocitrate:NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42)9 Together, however, they act in a concerted manner and strongly inhibit the enzyme. The rates of formation and dissociation of the enzyme inhibitor complex, and the rate of formation and the stability of the aldol condensation product of oxalacetate and glyoxylate, oxalomalate, were examined. The data obtained do not support the often suggested possibility that oxalomalate, per se, formed non-enzymatically in isocitrate dehydrogenase assay mixtures containing oxalacetate and glyoxylate, is responsible for the observed inhibition of the enzyme. Rather, the data presented in this communication suggest that oxalacetate binds to the enzyme first, and that the subsequent binding of glyoxylate leads to the formation of a catalytically inactive enzyme-inhibitor complex.
    Matched MeSH terms: Kinetics
  4. Law AT, Button DK
    Appl Environ Microbiol, 1986 Mar;51(3):469-76.
    PMID: 16347006
    Trace (microgram liter) quantities of either toluene or benzene injected into an amino-acid-limited continuous culture of Pseudomonas sp. strain T2 were utilized immediately with affinities of 2.6 and 6.8 liters g of cells h, respectively, and yielded large amounts of organic products, carbon dioxide, and cells. The immediate utilization of hydrocarbons by hydrocarbon-deprived organisms helps to establish the nutritional value of nonpolar substrates in the environment. The observation of small Michaelis constants for toluene transport led to tests of metabolic competition between hydrocarbons; however, competitive inhibition of toluene metabolism was not found for benzene, naphthalene, xylene, dodecane, or amino acids. Benzene and terpenes were inhibitory at milligram liter concentrations. Toluene was metabolized by a strongly inducible system when compared with benzene. The capacity of toluene to effect larger affinity values increased with exposure time and concentration. The kinetics of induction suggested saturation phenomena, resulting in an induction constant, K(ind), of 96 mug of toluene liter. Maximal induction of amino-acid-grown cells required about 80 h, with the affinity reaching 317 liters g of cells h.
    Matched MeSH terms: Kinetics
  5. Tan NH, Saifuddin MN
    PMID: 1982873
    1. The edema-inducing activity of 24 venoms from snakes of the subfamilies of Elapinae, Hydrophiini, Crotalinae and Viperinae was determined. 2. All snake venoms tested are very potent edema inducers. The minimum edema doses of the venoms ranged from 0.16 to 3.41 micrograms per mouse paw. 3. The venoms induced a rapid onset edema which peaked within 1 h of injection and declined thereafter; at low dose, however, some venoms induced a rapid onset edema that sustained over a longer duration.
    Matched MeSH terms: Kinetics
  6. Azila N, Othman I
    Biochem. Int., 1990;20(2):291-9.
    PMID: 1969267
    An extract prepared from the tentacle of Catostylus mosaicus was shown to lyse erythrocytes from rat, rabbit and human to a different extent; those from the rat being most susceptible followed by those from rabbit and human. The haemolytic activity was dependent on the concentration of crude extract protein exhibiting a sigmoidal curve. Only 60% of the haemolytic activity was retained after treament with heat and proteolytic enzyme. The extract was devoid of hydrolytic enzymes normally present in venoms except for phospholipase A activity, which resulted in the hydrolysis of membrane phospholipids with concomittant appearance of their lyso-derivatives.
    Matched MeSH terms: Kinetics
  7. Hashim OH, Hassan H
    Immunology, 1991 Jun;73(2):235-8.
    PMID: 2071167
    Three bacterial species of Clostridium (septicum, tertium and sporogenes) were identified to produce extracellular proteases cleaving IgA to Fab and Fc fragments, as demonstrated by SDS-PAGE and immunoelectrophoretic procedures. These enzymes acted on monometric IgA1 paraproteins and normal serum IgA1 but had no activity on IgA2 paraproteins and intact secretory IgA1 from human colostrum. Their action on polyclonal serum IgA1 suggested the absence of neutralizing anti-clostridial IgA protease activity. Although the enzymes were shown not to act on secretory IgA1, they were, however, able to digest free alpha-heavy chains of the dimeric IgA molecules. Susceptibility of the alpha-heavy chain to the proteases was more likely due to the change to a more accessible conformation than because of the absence of neutralizing anti-enzymic activity.
    Matched MeSH terms: Kinetics
  8. Tan IK, Ho CC
    Appl Microbiol Biotechnol, 1991 Nov;36(2):163-6.
    PMID: 1368105
    The utilisation of palm oil and its fractions by Penicillium chrysogenum for growth and penicillin production is strain-dependent. Strain H1107 could utilise crude palm oil, its liquid (palm olein) and solid (palm stearin) fractions and its component fatty acids (oleic, palmitic, stearic and myristic) as the main carbon source; strain M223 could not. Cell-bound lipase activity was higher in H1107 than in M223.
    Matched MeSH terms: Kinetics
  9. Azila N, Siao FK, Othman I
    PMID: 1675964
    1. An extract prepared from the tentacle of the jellyfish (CE), Catostylus mosaicus exhibited haemolytic, oedema and haemorrhage-inducing activities. 2. Acetone treatment of the tentacle extract produced an acetone soluble extract (AE) which showed an increase in specific haemolytic and haemorrhagic activities by 25- and 120-fold respectively; the minimum oedema dose was reduced by 30-fold. 3. The AE caused a rapid onset of oedema in the mouse foot pad. The effect was long-lasting, reaching a maximum in about 30 min after injection and sustained up to 4 hr. 4. Fractionation of the AE on Q-Sepharose gave 4 bound fractions which induced oedema and haemorrhage; however only 3 of the fractions exhibited haemolytic activity.
    Matched MeSH terms: Kinetics
  10. Nabishah BM, Morat PB, Kadir BA, Khalid BA
    Gen. Pharmacol., 1991;22(2):389-92.
    PMID: 1647349
    1. Glucocorticosteroid may relieve bronchospasm by mediating changes in the muscarinic receptor concentration and/or its affinity. 2. Cholinergic muscarinic receptors were determined by using Scatchard's plots from radioligand binding assays of 0.13-3.2 nM [3H]quinuclidinyl benzylate binding to the membrane fraction of bronchial smooth muscle (BSM). 3. The concentration of muscarinic receptor in BSM of normal rat was 57 +/- 3 fmol mg protein and the dissociation constant was 0.07 +/- 0.02 nM. Dexamethasone and corticosterone reduced muscarinic receptor concentration to 50-60% of basal with no changes in receptor affinity. No changes were found in rat treated with deoxycorticosterone. 4. These findings suggest that glucocorticoids but not mineralocorticoid relieve bronchospasm at least partly by reducing the cholinergic hypersensitivity.
    Matched MeSH terms: Kinetics
  11. Pang T, Devi S, Puthucheary S, Pawlowski N
    Microbiol. Immunol., 1991;35(3):267-71.
    PMID: 1870442
    Mouse macrophages pre-labeled with [3H]arachidonic acid (20:4) were shown to release metabolites generated by the lipoxygenase and cyclo-oxygenase pathways following in vitro addition of heat-killed Salmonella typhi. These metabolites were maximally released after 60-90 min of incubation and consisted of prostaglandins (85%), leukotriene C (6%), di-HETEs, leukotrienes D and E (4%), mono-HETEs (2%) and other metabolites (3%). Of the metabolites generated by the cyclo-oxygenase pathway (prostaglandins), 6-keto PGF1 alpha and PGE2 were generated at a ratio of 1.2 to 1. The significance and importance of these results are discussed.
    Matched MeSH terms: Kinetics
  12. Tan NH, Saifuddin MN
    Int. J. Biochem., 1991;23(3):323-7.
    PMID: 2044840
    1. Substrate specificity of purified king cobra (Ophiophagus hannah) venom L-amino acid oxidase was investigated. 2. The enzyme was highly specific for the L-enantiomer of amino acid. Effective oxidation of L-amino acid by the enzyme requires the presence of a free primary alpha-amino group but the alpha-carboxylate group is not as critical for the catalysis. 3. The enzyme was very active against L-Lys, L-Phe, L-Leu, L-Tyr, L-Tryp, L-Arg, L-Met, L-ornithine, L-norleucine and L-norvaline and moderately active against L-His, L-cystine and L-Ileu. Other L-amino acids were oxidized slowly or not oxidized. 4. The data suggest the presence of a side chain binding site in the enzyme, and that the binding site comprises at least five 'subsites': the hydrophobic subsites a, b and c; and the two 'amino' binding subsites d and e. Subsite b appears to be able to accommodate two methylene/methyl carbons.
    Matched MeSH terms: Kinetics
  13. Hashim OH, Gendeh GS, Jaafar MI
    Biochem. Int., 1992 Jun;27(1):139-43.
    PMID: 1627170
    The effect of extracts of champedak (Artocarpus integer) seed lectin on the proliferation of normal human lymphocyte was investigated. The IgA1 binding lectin was demonstrated to stimulate the proliferation of human peripheral blood mononuclear cells. Action of the lectin on enriched T and B cell populations demonstrated T lymphocyte specificity. The lectin was not mitogenic to B lymphocytes. Optimal stimulation of proliferative response was achieved when cells were subjected to 5 days exposure to the crude lectin at 20 micrograms/ml.
    Matched MeSH terms: Kinetics
  14. Tan NH, Swaminathan S
    Int. J. Biochem., 1992 Jun;24(6):967-73.
    PMID: 1612186
    1. The L-amino acid oxidase of the monocellate cobra (Naja naja kaouthia) venom was purified to electrophoretic homogeneity. The molecular weight of the enzyme was 112,200 as determined by Sephadex G-200 gel filtration chromatography, and 57,400 as determined by SDS-polyacrylamide gel electrophoresis. 2. The enzyme had an isoelectric point of 8.12 and a pH optimum of 8.5. It showed remarkable thermal stability, and, unlike many venom L-amino acid oxidase, was also stable in alkaline medium. The enzyme was partially inactivated by freezing. 3. The enzyme was very active against L-phenylalanine and L-tyrosine, moderately active against L-tryptophan, L-methionine, L-leucine, L-norleucine, L-arginine and L-norvaline. Other L-amino acids were oxidized slowly or not oxidized. 4. Kinetic studies suggest the presence of a side-chain binding site in the enzyme, and that the binding site comprises of at least four hydrophobic subsites.
    Matched MeSH terms: Kinetics
  15. Ampon K
    J Chem Technol Biotechnol, 1992;55(2):185-90.
    PMID: 1384564
    Trypsin has been immobilized by adsorption onto Amberlite XAD-7 beads. The Michaelis constant (Km) of the enzyme was increased about sevenfold following the immobilization. Its rate of penetration into the porous beads was determined by staining the beads, which had been split, with naphthol blue black. The extent of diffusional rate limitation of immobilized trypsin was related to the penetration depth of the enzyme into the beads. This can be controlled by manipulating the conditions during the preparation of the immobilized enzyme.
    Matched MeSH terms: Kinetics
  16. Lee PM, Lee KH, Siaw YS
    J Chem Technol Biotechnol, 1993;58(1):65-70.
    PMID: 7763937
    Aminoacylase I (EC. 3.5.1.14) was immobilized by covalent crosslinking to alginate molecules with 1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide HCl followed by calcium alginate bead formation for the production of L-phenylalanine from the racemic mixtures of N-acetyl-DL-phenylalanine. Different concentrations of the coupling reagent were tested and the coupling process was optimized. The immobilized and the partially purified aminoacylase were characterized in terms of the activity, operational stability, thermal stability, pH and temperature optima and kinetic constants, Km and Vmax. The activity of the enzyme covalently immobilized in calcium alginate beads was enhanced by about 75% compared to that of free enzyme. The beads showed stable activity under operational conditions, they lost about 40% of their activity after four reaction cycles. The immobilized aminoacylase was more stable over a broader pH range. Thus this simple method provides irreversible immobilization of aminoacylase to give a biocatalyst with good operational stability and enhanced activity.
    Matched MeSH terms: Kinetics
  17. Lee KH, Lee PM, Siaw YS
    J Chem Technol Biotechnol, 1993;57(1):27-32.
    PMID: 7763683
    Aminoacylase I (EC 3.5.1.14) encapsulated in calcium alginate beads stabilized with poly-L-lysine was used for the production of L-phenylalanine by the hydrolysis of a racemic mixture of N-acetyl-DL-phenylalanine. The immobilized aminoacylase was studied with respect to operational stability, thermal stability, effects of pH and temperature and kinetic constants. The leakage of enzyme from the stabilized beads was eliminated. The immobilized enzyme retained high biological activity. The Km and Vmax values for the stabilized beads were 11.11 mmol dm-3 and 0.076 mumol min-1 respectively. The optimum pH and temperature for the hydrolysis were 6.5 and 55 degrees C respectively. Scanning electron micrographs revealed crosslinked structures on the surface of the beads. The operational performances of the beads in a batch reaction and a packed-bed bioreactor for continuous reaction were investigated. With batch reaction, only about 5% of enzyme activity was lost within ten reaction cycles and there was no significant loss of activity over 600 h of continuous operation after equilibrium was reached, and a conversion yield of about 80% was obtained.
    Matched MeSH terms: Kinetics
  18. Lee PM, Lee KH, Siaw YS
    PMID: 8260581
    Aminoacylase I (E.C.3.5.1.14) was immobilized by entrapment in calcium alginate beads coated with polyethyleneimine for the production of L-phenylalanine by the hydrolysis of a racemic mixture of N-acetyl-DL-phenylalanine. The operational stability in terms of batch operation and continuous reaction in packed-bed bioreactor were studied. Kinetic constants, Km and Vmax values of free and immobilized enzymes were studied. Polyethyleneimine treatment was found to enhance the operational stability of the enzyme though its activity was substantially reduced. When polyethyleneimine-coated calcium alginate beads were packed into packed bed bioreactor, it was stable for at least 25 days under continuous operation without appreciable loss of activity.
    Matched MeSH terms: Kinetics
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