Manganese ions enzyme activators

Manganese ions enzyme activators, 6,578 probes, 6,563 RNA polymerases activation, 6, 585 transport microbes, 6, 569 plants, 6, 572 Manganese oxide colloidal... 

Mounter and his co-workers3 designate this enzyme responsible for the hydrolysis of D.F.P. as dialkylfluorophosphatase (D.F.P.-ase). They have shown that D.F.P.-ase from hog kidney is activated by cobalt and manganese ions. In the presence of... 

Many proteins, including many enzymes, contain hghtly bound metal ions. These may be inhmately involved in enzyme catalysis or may serve a purely structural role. The most common tightly bound metal ions found in metalloproteins include copper (Cu+ and Cu +), zinc (Zn +), iron (Fe + and Fe +), and manganese (Mn +). Other proteins may contain weakly bound metal ions that generally serve as modulators of enzyme activity. These include sodium (Na+), potassium (K+), calcium (Ca +), and magnesium (Mg +). There are also exotic cases for which enzymes may depend on nickel, selenium, molybdenum, or silicon for activity. These account for the very small requirements for these metals in the human diet. 

The enzyme that catalyzes reaction 7 has been solubilized, 4" 141 and purified141 2000-fold. The enzyme activity is dependent on manganese ions. The enzymes catalyzing reactions 5 and 6 have not yet heen solubilized, purified, or separated, and, therefore, the substrate specificities indicated remain speculative. 

An ATP-dependent DNase has been partially purified from extracts of E. coli by Oishi (86) and Barbour and Clark (37). It shows an absolute requirement for magnesium or manganese ion and has a broad pH optimum ranging from pH 7.5 to 9.5. The partially purified enzyme preferentially degrades native DNA (including glucosylated T4 DNA) and has an almost absolute requirement for ATP or dATP. Current preparations of the enzyme are also active on denatured DNA however, there is only a slight stimulation of hydrolysis by added ATP. This latter activity may therefore represent some contamination with exonuclease I. The mode of attack is stated to be exonucleolytic. 

Magnesium (manganese) and calcium ions as enzyme activators 565... 

Not surprisingly, both manganese ions are necessary for the catalase activity of arginase, as confirmed by metal replacement experiments in a mutant arginase. Indeed, whereas the hydrolytic reaction was restored upon binding one Cd2+ ion to form a heteronuclear MnCd enzyme, catalase activity was not [111]. 

The enzyme responsible for the photolysis of water in plants is a multisubunit membrane protein (Fig. 5-22 Klein et al., 1991). Four manganese ions, probably as a tetranuclear cluster, are thought to act as a charge accumulating system and as the active site for water oxidation. Both calcium and chloride ions are also required for activity (Babcock, 1987 Ghantokakis and Yocum, 1990). The water oxidation centre (WOC) contains a total of four Mn atoms and causes the oxidative coupling of two water molecules by a currently unknown mechanism. 

Manganese ions, Mn2+ Present in some enzymes, it activates blood haemoglobin synthesis, urea formation, growth, reproduction processes and release of insulin. Manganese ions also take part in enzyme control in the brain Zinc ions, Zn2+ Small quantities help carbon dioxide metabolism and removal. Zinc is... 

CD spectroscopy has also been used to study the metal-binding and reactivity properties of iron- and manganese-containing SODs. These enzymes metabolize the superoxide ion radical O2 into molecular oxygen and hydrogen peroxide. The Fe- and Mn-SOD enzymes are strictly metal specific. Jackson and Brunold show that, despite the fact that Fe replacement of Mn in the Mn-SOD enzyme [(Mn Fe)-SOD] results in an inactive enzyme, the CD spectrum of wild-type Fe-SOD and (Mn - Fe)-SOD are remarkably similar. This suggests that the destroyed enzyme activity, upon replacement of the metal, does not occm via distortion of the enzyme active site. 

Pyruvate carboxylase is a well-known Mn metalloenzyme. The enzyme is a tetramer and contains one biotin cofactor per subunit and one divalent cation per subunit. The enzyme from calf liver, for example, contains four tightly boimd Mn atoms. The enzyme from chicken liver contains two Mn atoms and two Mg atoms. Raising chickens on an Mn-deficient diet results in the production of an Mn-free enzyme, where magnesium ions replace the usually occurring manganese ions. The Mg-containing enzyme is catalytically active, leaving the requirement of the enzyme for Mn in question (Scrutton et al, 1972). 

Manganese is a constituent of many important metalloen-zymes and also acts as a nonspecific enzyme activator. Mn " ions can be replaced by Mg, Co % and other cations during the activation of some enzymes. Some important manganese-dependent enzymes are discussed below. 

Pyruvate Carboxylase. This enzyme has manganese firmly in its structure and acts together with phosphoenol pyruvate (PEP) carboxykinase, an enzyme that is activated by manganese ions. These enzymes are required to catalyze the formation of PEP from pyruvate, a key reaction in the hepatic synthesis of glucose. 

Manganese superoxide dismutase (MnSOD) is a redox-active manganese enzyme that employs a mononuclear manganese ion at its active site. Discovered in 1970 (52), this enzyme catalyzes the dismuta-tion of superoxide (H02), to dioxygen and hydrogen peroxide, as shown in Scheme 2. Superoxide is the radical, one-electron-reduced... 

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