Biomaterial Database

Zinc and cadmium 5-aminolevulinate dehydratase. Metal-dependent pH profiles. 1987

M Schlösser, and D Beyersmann

Fachbereich Biologie/Chemie, Universität Bremen.

Native 5-aminolevulinic acid dehydratase contains zinc ions, which are essential for the enzymatic activity. Replacement of zinc by cadmium yielded an active enzyme whose kinetic parameters (kkat and Km) are similar to those of the zinc enzyme in the neutral pH range. However, the pH profiles of kcat and Km were different due to different pKa values. Two groups both with pKa values of 6.5 in the free zinc enzyme, but with pKa values of 7.0 in the cadmium enzyme were calculated from plots of log (kcat/Km) versus pH. On the other hand, the enzyme-substrate complex is controlled by one acidic group (zinc pKa = 6.0, cadmium pKa = 6.4) and one basis group (zinc pKa = 8.2, cadmium pKa = 7.7) as calculated from plots of log kcat versus pH. The Arrhenius plots for kcat of the two enzymes show no significant difference, the free energies of activation are 77.1 kJ/mol for the zinc and 76.8 kJ/mol for the cadmium enzyme. From this and from previous work it is concluded that the metal ions are located near the active site and influence the ionisations of essential amino acid residues. From the pH profiles of the modifying reaction and inhibition by diethylpyrocarbonate a histidinyl residue is inferred as one of the ionisable groups of the active site.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D002104	Cadmium	An element with atomic symbol Cd, atomic number 48, and atomic weight 112.41. It is a metal and ingestion will lead to CADMIUM POISONING.
D004795	Enzyme Stability	The extent to which an enzyme retains its structural conformation or its activity when subjected to storage, isolation, and purification or various other physical or chemical manipulations, including proteolytic enzymes and heat.	Enzyme Stabilities,Stabilities, Enzyme,Stability, Enzyme
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
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
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures
D013816	Thermodynamics	A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)	Thermodynamic
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.