Biomaterial Database

Investigation of the effect of metal ions on the reactivity of thiol groups in human 5-aminolaevulinate dehydratase. 1985

P N Gibbs, and M G Gore, and P M Jordan

The reaction of human 5-aminolaevulinate dehydratase with 5,5'-dithiobis-(2-nitrobenzoic acid) (Nbs2) results in the release of 4 molar equivalents of 5-mercapto-2-nitrobenzoic acid (Nbs) per subunit. Two of the thiol groups reacted very rapidly (groups I and II), and their rate constants were determined by stopped-flow spectrophotometry; the other two thiol groups (groups III and IV) were observed by conventional spectroscopy. Titration of the enzyme with a 1 molar equivalent concentration of Nbs2 resulted in the release of 2 molar equivalents of Nbs and the concomitant formation of an intramolecular disulphide bond between groups I and II. Removal of zinc from the holoenzyme increased the reactivity of groups I and II without significantly affecting the rate of reaction of the other groups. The reactions of the thiol groups in both the holoenzyme and apoenzyme were little affected by the presence of Pb2+ ions at concentrations that strongly inhibit the enzyme, suggesting that Zn2+ and Pb2+ ions may have independent binding sites. Protein fluorescence studies with Pb2+ and Zn2+ have shown that the binding of both metal ions results in perturbation of the protein fluorescence.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D007854	Lead	A soft, grayish metal with poisonous salts; atomic number 82, atomic weight 207.2, symbol Pb.
D004228	Dithionitrobenzoic Acid	A standard reagent for the determination of reactive sulfhydryl groups by absorbance measurements. It is used primarily for the determination of sulfhydryl and disulfide groups in proteins. The color produced is due to the formation of a thio anion, 3-carboxyl-4-nitrothiophenolate.	5,5'-Dithiobis(2-nitrobenzoic Acid),DTNB,Ellman's Reagent,5,5'-Dithiobis(nitrobenzoate),Acid, Dithionitrobenzoic,Ellman Reagent,Ellmans Reagent,Reagent, Ellman's
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000623	Porphobilinogen Synthase	An enzyme that catalyzes the formation of porphobilinogen from two molecules of 5-aminolevulinic acid. EC 4.2.1.24.	Aminolevulinate Hydro-Lyase,Aminolevulinic Acid Dehydratase,ALA-Dehydrase,delta-Aminolevulinate Dehydratase,delta-Aminolevulinic Acid Dehydratase,ALA Dehydrase,Acid Dehydratase, Aminolevulinic,Acid Dehydratase, delta-Aminolevulinic,Aminolevulinate Hydro Lyase,Dehydratase, Aminolevulinic Acid,Dehydratase, delta-Aminolevulinate,Dehydratase, delta-Aminolevulinic Acid,Hydro-Lyase, Aminolevulinate,Synthase, Porphobilinogen,delta Aminolevulinate Dehydratase,delta Aminolevulinic Acid Dehydratase
D001051	Apoenzymes	The protein components of enzyme complexes (HOLOENZYMES). An apoenzyme is the holoenzyme minus any cofactors (ENZYME COFACTORS) or prosthetic groups required for the enzymatic function.	Apoenzyme
D013050	Spectrometry, Fluorescence	Measurement of the intensity and quality of fluorescence.	Fluorescence Spectrophotometry,Fluorescence Spectroscopy,Spectrofluorometry,Fluorescence Spectrometry,Spectrophotometry, Fluorescence,Spectroscopy, Fluorescence
D013053	Spectrophotometry	The art or process of comparing photometrically the relative intensities of the light in different parts of the spectrum.
D013438	Sulfhydryl Compounds	Compounds containing the -SH radical.	Mercaptan,Mercapto Compounds,Sulfhydryl Compound,Thiol,Thiols,Mercaptans,Compound, Sulfhydryl,Compounds, Mercapto,Compounds, Sulfhydryl
D015032	Zinc	A metallic element of atomic number 30 and atomic weight 65.38. It is a necessary trace element in the diet, forming an essential part of many enzymes, and playing an important role in protein synthesis and in cell division. Zinc deficiency is associated with ANEMIA, short stature, HYPOGONADISM, impaired WOUND HEALING, and geophagia. It is known by the symbol Zn.