Manganese-containing enzyme

S / V CONTENTS Preface, Robert W. Hay. Structure and Function of Manganese-Containing Biomolecules, David C. Weather-bum. Repertories of Metal Ions as Lewis Acid Catalysts in Organic Reactions, Junghan Suh. The Multicopper-Enzyme Ascorbate Oxidase, Albrecht Messerschmidt. The Bioinorganic Chemistry of Aluminum, Tomas Kiss and Etelka Farkas. The Role of Nitric Oxide in Animal Physiology, Anthony R. Butler, Frederick Flitney and Peter Rhodes. Index. 

A manganese-containing YADH has been obtained from yeast grown in a zinc-free, manganese-rich medium.12 4 The enzyme was found to have four atoms of metal per enzyme molecule, all of which were manganese. This manganese enzyme is much less stable than the native zinc enzyme and the kinetic parameters are different. 

Purple, iron-containing acid phosphatases have been purified from animal sources and from some plant sources.350 However, the purple acid phosphatase from the sweet potato contains manganese, the purple colour arising from an intense absorption band at about 515 nm. There is some doubt over the stoichiometry, in that the dimeric enzyme may contain one351 or two352 Mn2+, apparently depending on the variety of sweet potato. The iron acid phosphatases contain two Fe atoms. 

The isolation of the first manganese-containing acid phosphatase was reported in 1971 from the juice of the sweet potato (Kokei No. 14) (67). The enzyme was unique in that it was distinctly purple, the color resulting from a broad absorption band with a maximum at 555 nm. The enzyme was determined to be 110 kDa, composed of two 55-kDa subunits. The purple enzyme was capable of hydrolyzing a variety of biologically relevant phosphates as well as inorganic pyrophosphate [Eq. (2)]. Emission spectroscopy revealed the presence of Mn (68). 

Subsequently, a manganese-containing catalase has been isolated from the aerobic bacterium Thermoleophilum album (162). The enzyme is 141 kDa and is composed of four subunits of 34 kDa. There were 1.4 + 0.4 atoms of manganese present per subunit. The enzyme could be inhibited by NH2OH but only weakly inhibited by cyanide or azide. The enzyme was colorless at concentrations of 0.7 mg/ml. 

SODl copper and zinc containing form of superoxide dismutase, a superoxide anion scavenging enzyme SOD2 manganese containing form of superoxide dismutase localized in the mitochondrial matrix... 

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. 

In recent years. X-ray crystallography has led to the discovery of several novel metalloclusters of complex architecture that contain at least four metal ions (4, 5). They represent the active site of several redox enzymes that contain molybdenum, nickel, and manganese, as well as the most commonly encountered iron and copper (Fig. 6). These enzymes are extremely specialized in the oxidation or reduction reactions of the smallest molecules and anions (which include N2, CO, and H2). A common feature of such clusters is that they are present in enzymes as part of a more extensive electron transfer chain that involves a series of... 

Eukaryotes contain two forms of this enzyme, a manganese-containing version located in mitochondria and a copper-zinc-dependent cytosolic form. These enzymes perform the dismutation reaction by a similar mechanism (Figure 18.22). The oxidized form of the enzyme is reduced by superoxide to form oxygen. The reduced form of the enzyme, formed in this reaction, then reacts with a second superoxide ion to form peroxide, which takes up two protons along the reaction path to yield hydrogen peroxide. 

The effect of ischemia-reperfusion injury on activity, protein and m-RNA levels of proteins is also studied. For example, the enzymes that are involved in free radical detoxication (catalase, copper-zinc and manganese containing superoxide dismutase and glutatione peroxidase) were studied in rat kidney [101]. This study... 

These dismutases are still poorly characterized. Table 27 lists details of both iron- and manganese-containing enzymes. The manganese dismutases contain Mn ", and occur either as dimers or tetramers with subunits of molecular weight about 20 000. The Mn/subunit ratio varies from 0.5 through 1.0 to 2.0. The iron dismutases have subunits of 20 000 or 40 000 and an upper limit of one Fe" per subunit. It has been pointed out that most of the proteins are synthesized initially as precursors, which are between 2000 and 6000 larger in molecular weight than that of the mature protein. 

Iizuka, S., Taniguchi, N., and Makita, A., Enzyme-linked immunosorbent assay for human manganese-containing superoxide dismutase and its content in lung cancer. JNCI, J. Natl. Cancer Inst. 72, 1043-1049 (1984). 

K7. Keele, B. B., McCord, J. M., and Fridovich, I., Superoxide dismutase from Escherichia coli B. A new manganese-containing enzyme. J. Biol. Chem. 245, 6176-6181 (1970). 

Manganese complexes as models for manganese-containing pseudocatalase enzymes Synthesis, structural and catalytic activity studies... 

The chlorophyll ion in P680+ takes electrons from water, via a manganese-containing enzyme complex, and is reduced to the neutral unexcited state, ready to pick up new photons. Water is then split to oxygen and hydrogen ions. Oxygen is a toxic waste product, while the hydrogen ions contribute to the buildup of the pH difference across the membrane. 

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