Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

At pH 4.1, bovine thrombin reacts rapidly with N-bromo-succinimide to yield modified enzyme containing oxidized tryptophan residue. Both fibrinogen clotting activity and esterase activity are reduced considerably when three moles of tryptophan residues per mole of thrombin are oxidized, but the Michaelis constants for synthetic substrates are not appreciably altered. Reaction of NBS also results in a decrease in the affinity of thrombin for heparin. The dissociation constant for heparin-thrombin complex is increased by 2.6-fold due to the modification of one tryptophan residue. However, the magnitude of the increase in the dissociation constant remains the same for modified enzymes containing approximately two or three oxidized tryptophan residues. The rate constant for the inactivation of thrombin by antithrombin III is increased by 2.5-fold due to the modification of a single tryptophan residue. This increase in rate constant is not further amplified when more than one tryptophan residue is oxidized. In contrast, in the presence of heparin the rate of inactivation of modified and unmodified thrombins by antithrombin III are not significantly different. Thus, the heparin-sensitized inactivation of thrombin by antithrombin III is affected by the modification of one tryptophan residue. Spectrophotometric titrations of the phenolic hydroxyl groups suggest that the structural environments of tyrosyl groups for both unmodified and modified thrombin containing one oxidized tryptophan residue, are similar. The temperature for half loss of catalytic activity of control and NBS-modified thrombin, containing one oxidized tryptophan, are 52 and 51.5 degrees C respectively. It appears that the one tryptophan residue of thrombin is situated at or close to the binding site of heparin.
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PMID:Catalytic and regulatory functions of N-bromosuccinimide-modified bovine thrombin. 652 42

Carboxymethylcellulase (CMCase) was extracted and purified from an angiosperm parasite Cuscuta reflexa free from beta-glucosidase and other enzyme activities. The molecular mass and Stokes' radius of the purified enzyme are 144 kDa and 44 A, respectively. The diffusion coefficient and frictional ratio of the enzyme were 5.15 x 10(-7) cm2/sec and 1.27. The SDS-PAGE revealed homotetrameric nature of the enzyme with a subunit molecular mass of 35 +/- 1 kDa. Titration against DTNB and NBS revealed 19 sulfhydryl groups and 8 tryptophan groups, respectively, per mole of the enzyme. A sharp pH optimum at 5.0 was obtained. Cuscuta CMCase activity is unique amongst plant endoglucanases in being stimulated by Mg2+ and Mn2+ ions and by various thiols. Reaction product analysis, mode of enzyme action and substrate specificity test suggest the endo- nature of the purified CMCase. The enzyme showed K(m) value of 26 +/- 1 mg/ml for carboxymethylcellulose (sodium salt).
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PMID:Physico-chemical and functional characterization of a high molecular weight carboxymethylcellulase from Cuscuta reflexa. 949 45

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.
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PMID:Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil. 1460 17

A specimen of 4-aminopyridine purified by repeated sublimation in an atmosphere of nitrogen has been titrated coulometrically in two ways: (1) directly, using the hydrazine-platinum anode, and (2) with perchloric acid, the titration being completed coulometrically and the perchloric acid being standardized coulometrically. The values for the faraday calculated from these titrations are 96,486.40 (1.53) and 96,486.78 (0.57), 1972 NBS coulombs per mole, respectively, the average being 96,486.69 (0.81) and the numbers in the parentheses the standard deviations. The maximum error obtained by combining the estimated maximum errors in the various measurements was 8.4 ppm.
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PMID:A high-precision titration of 4-aminopyridine A value for the faraday. 1896 18