For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

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Structural and Functional Aspects of Metal Sites in Biology

Neutrophilic polymorphonuclear leukocytes (neutrophils) are highly specialized for their primary function, the phagocytosis and destruction of microorganisms. When coated with opsonins (generally complement and/or antibody), microorganisms bind to specific receptors on the surface of the phagocyte and invagination of the cell membrane occurs with the incorporation of the microorganism into an intracellular phagosome. There follows a burst of oxygen consumption, and much, if not all, of the extra oxygen consumed is converted to highly reactive oxygen species. In addition, the cytoplasmic granules discharge their contents into the phagosome, and death of the ingested microorganism soon follows. Among the antimicrobial systems formed in the phagosome is one consisting of myeloperoxidase (MPO), released into the phagosome during the degranulation process, hydrogen peroxide (H2O2), formed by the respiratory burst and a halide, particularly chloride. The initial product of the MPO-H2O2-chloride system is hypochlorous acid, and subsequent formation of chlorine, chloramines, hydroxyl radicals, singlet oxygen, and ozone has been proposed. These same toxic agents can be released to the outside of the cell, where they may attack normal tissue and thus contribute to the pathogenesis of disease. This review will consider the potential sources of H2O2 for the MPO-H2O2-halide system; the toxic products of the MPO system; the evidence for MPO involvement in the microbicidal activity of neutrophils; the involvement of MPO-independent antimicrobial systems; and the role of the MPO system in tissue injury. It is concluded that the MPO system plays an important role in the microbicidal activity of phagocytes.

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Myeloperoxidase: friend and foe

Mechanisms and applications of plant growth promoting rhizobacteria: Current perspective

ion from the Sugar Moiety Wendy Knapp Pogozelski† and Thomas D. Tullius*,‡ Department of Chemistry, State University of New York at Geneseo, Geneseo, New York 14454, and Department of Chemistry, Boston University, Boston, Massachusetts 02215 Received August 27, 1997 (Revised Manuscript Received February 26, 1998)

Oxidative Strand Scission of Nucleic Acids: Routes Initiated by Hydrogen Abstraction from the Sugar Moiety.

On the function and mechanism of action of peroxidases

Oxygen in the gas vacuole of the rhizopod protozoan, arcella.

Crystallization of a complex of hemoglobin components II and III of the symbiont-harboring clam Lucina pectinata.

A hemeprotein implicated in oxygen transport into the eye of fish

Toadfish (Opsanus tau) essentially lacking circulating erythrocytes were pre pared by repeated exchange transfusion with serum. The rate of nitrogen secretion is not changed by removal of the erythrocytes. Oxygen secretion is slowed dras tically. This shows that nitrogen secretion does not require erythrocytes and is not driven by oxygen secretion. In the absence of circulating erythrocytes, oxygen and nitrogen are brought into the swimbladder in proportion to their concentrations in blood plasma. Carbon dioxide partial pressure in the secreted gas mixture is three to fourfold greater than the pressure generated by acidifying arterial blood. This implies counter-current multiplication of the small increment of carbon dioxide pressure brought about by acidification of the blood. In the presence of blood buffers, increased carbon dioxide pressure will increase blood bicarbonate. Three independent estimates indicate that, during gas secretion, gas gland blood is near pH 6.5. Total carbon dioxide (CO2, HCO3, CO3) is increased from the arterial value near 2 mM to about 14 mM, divided nearly equally between carbon dioxide and bicarbonate anion. The increment in total blood carbon dioxide concentration together with the well-known increment in lactate anion may serve to salt out inert gases from solution in blood plasma.

Jonathan B. Wittenberg

Papers

Oxygen in the gas vacuole of the rhizopod protozoan, arcella.

Crystallization of a complex of hemoglobin components II and III of the symbiont-harboring clam Lucina pectinata.

A hemeprotein implicated in oxygen transport into the eye of fish

Secretion of nitrogen into the swimbladder of fish. i. secretion by fishes nearly lacking circulating hemoglobin. role of the rete mirabile

Oxygen binding by hemoglobin of the galapagos rift vent worm Riftia pachyptila Jones (Pogonophora; Vestimentifera)