Biomaterial Database

Mg2+ is an essential activator of hydrolytic activity of membrane-bound pyrophosphatase of Rhodospirillum rubrum. 1992

A Sosa, and H Ordaz, and I Romero, and H Celis

Departamento de Bioenergética, Universidad Nacional Autóoma de México, D.F.

The substrate for the hydrolytic activity of membrane-bound pyrophosphatase is the PP(i)-Mg2+ complex. The enzyme has no activity when the free Mg2+ concentration is lower than 10 microM (at 0.5 mM-PP(i)-Mg2+), and therefore free Mg2+ is an essential activator of the hydrolytic activity. The Km for the substrate changes in response to variation in free Mg2+ concentration, from 10.25 to 0.6 mM when free Mg2+ is increased from 0.03 to 1.0 mM respectively. The Km for Mg2+ depends on the substrate concentration: the Km decreases from 0.52 to 0.14 mM from 0.25 to 0.75 mM-PP(i)-Mg2+ respectively. The extrapolated Km for Mg2+ in the absence of the substrate is 0.73 mM. Imidodiphosphate-Mg2+ and free Ca2+ were used as competitive inhibitors of substrate and activator respectively. The equilibrium binding kinetics suggest an ordered mechanism for the activator and the substrate: Mg2+ ions bind the enzyme before PP(i)-Mg2+ in the formation of the catalytic complex, membrane-bound pyrophosphatase-(Mg2+)-(PP(i)-Mg2+).

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008274	Magnesium	A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.
D011755	Pyrophosphatases	A group of enzymes within the class EC 3.6.1.- that catalyze the hydrolysis of diphosphate bonds, chiefly in nucleoside di- and triphosphates. They may liberate either a mono- or diphosphate. EC 3.6.1.-.	Pyrophosphatase
D004789	Enzyme Activation	Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme.	Activation, Enzyme,Activations, Enzyme,Enzyme Activations
D012247	Rhodospirillum rubrum	Vibrio- to spiral-shaped phototrophic bacteria found in stagnant water and mud exposed to light.
D043564	Inorganic Pyrophosphatase	An enzyme which catalyzes the hydrolysis of diphosphate (DIPHOSPHATES) into inorganic phosphate. The hydrolysis of pyrophosphate is coupled to the transport of HYDROGEN IONS across a membrane.	Pyrophosphatase, Inorganic,H(+)-PPase,H+-Pyrophosphatase,Proton-Pumping Inorganic Pyrophosphatase,Proton-Translocating Pyrophosphatase,Pyrophosphate-Energized Inorganic Pyrophosphatase,H+ Pyrophosphatase,Inorganic Pyrophosphatase, Proton-Pumping,Inorganic Pyrophosphatase, Pyrophosphate-Energized,Proton Pumping Inorganic Pyrophosphatase,Proton Translocating Pyrophosphatase,Pyrophosphatase, Proton-Pumping Inorganic,Pyrophosphatase, Proton-Translocating,Pyrophosphatase, Pyrophosphate-Energized Inorganic,Pyrophosphate Energized Inorganic Pyrophosphatase
D020130	Bacterial Chromatophores	Organelles of phototrophic bacteria which contain photosynthetic pigments and which are formed from an invagination of the cytoplasmic membrane.	Chromatophores, Bacterial,Bacterial Chromatophore,Chromatophore, Bacterial