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

NMR spectroscopy in the structural elucidation of oligosaccharides and glycosides.

Publisher Summary This chapter provides an overview of the 13 Carbon-nuclear magnetic resonance ( 13 C-NMR) spectroscopy of monosaccharides. The 13 C-NMR spectroscopy has become increasingly important as a tool for the characterization and structural elucidation of sugars and their derivatives. Although 13 C-NMR is closely related to 1 H-NMR spectroscopy, especially when both types of spectra are recorded with Fourier-transform instruments, the two techniques are sufficiently different to be valuable complements to each other. In many cases, in particular when dealing with complex molecules such as polysaccharides, the amount of information obtainable from 1 H-NMR spectra is limited as compared to that revealed by 13 C- NMR spectra. This chapter provides an almost complete collection of 13 C- NMR chemical shifts of monosaccharides, their methyl glycosides, and acetates, along with the examples of shift data for as many different types of monosaccharide derivative as possible. It also provides details on sampling techniques and assignment techniques, and discusses the identity of monosaccharides, their structure determination, and conformational analysis .

Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Monosaccharides

Zinc enzymology is, compared to some other current areas of metallobiochemistry, a maturing field, but in addition to further developments of structure-function relationships it has also provided a number of surprising new results and ideas in the last few years. In fact, the number of studies makes it impossible to provide a comprehensive review of the recent literature on zinc enzymology here, and the authors therefore focus on those zinc enzymes for which structure-function relationships are possible on the basis of structural and biochemical data. This means that, with a few exceptions, only zinc enzymes for which NMR or crystal structures are available are included here. Another seemingly simple, yet experimentally sometimes complex issue concerns the choice of which metalloenzyme is a zinc enzyme. Since there is in principle no difference in chemical catalysis by low-affinity compared to high-affinity metal sites, some of these enzymes are also included in this article, especially if they are or have been discussed as zinc enzymes, or are active with zinc. 552 refs.

Recent Advances in Zinc Enzymology

I. Vitamin D Endocrine System RESEARCH directed at defining the molecular mode of action of vitamin D is currently at its apex. There is now evidence implicating the essential involvement of vitamin D metabolites in a host of cellular processes, including calcium homeostasis, immunology, cell differentiation, and regulation of gene transcription. Further, there is evidence that the hormonally active form of vitamin D, 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], may generate biological responses via both regulation of gene transcription as well as via nongenomic pathways, some of which involve opening of voltage-gated Ca2+ channels. In addition, there are many examples of pathological disruption of the normal state in which a drug form of a vitamin D metabolite is proposed to be a (potentially) useful form of treatment, e.g. renal osteodystrophy, psoriasis, leukemia, breast cancer, and osteoporosis. B. From vitamin to steroid hormone The importance of the molecule vitamin D in the biological systems of highe...

Structure-Function Relationships in the Vitamin D Endocrine System*

Proton decoupled and undecoupled 13C n.m.r. spectra have been measured on a number of hexopyranoses. The direct coupling constants between the anomeric carbon atoms and protons {1J[13C–H(1)]} were found to be ca. 160 in the β-anomers and ca. 170 Hz in the α-anomers; the difference of ca. 10 Hz between pairs of anomers was found in almost all cases. Chemical shifts and 1J(13CH) values of the other carbon atoms in the pyranose rings were also measured.

A study of 13CH coupling constants in hexopyranoses

Publisher Summary This chapter presents a compilation of 13 C-nuclear magnetic resonance (NMR) data for oligosaccharides in the form of tables. The literature-survey presented in the chapter covers most of the data of 1982, and all of the information given had been measured for solutions in D 2 O unless stated otherwise. The data for peracetates of xylobioses and of glucobioses were recorded for solutions in CDCl 3 . All data have been copied from the original articles. For mutarotated mixtures of trisaccharides and larger oligosaccharides, the complete set of data is given for the α anomer, but only the chemical shifts for the reducing end of the anomer are given, provided that all other chemical shifts (for the remaining units) are identical. The sampling and assignment techniques used for the measurement of 13 C-NMR spectra of oligosaccharides are identical to those for monosaccharides. Particularly for oligosaccharides, it is important to measure the spectra at the same temperature—that is, with a precision better than ±0.5 p.p.m., when data are to be compared accurately.

Carbon-13 nuclear magnetic resonance data for oligosaccharides

Hard-sphere (HS) calculations predict three conformers for the branched B human blood group antigenic determinant (α LFuc(1 → 2)[α DGal(1 → 3)]βDGal) and two conformers for the linear tetrasaccharide (αLRha(1 → 2)αLRha(1 → 3)αLRha(1 → 3)βDGlcNAc), which constitutes a part of the repeating unit of the Shigellaflexneri O-antigen, which differ in conformational energy by less than 0.7 and 0.2 kcal/mol, respectively. However, a detailed 1H nmr study of specific interunit deshielding effects, quantitative treatment of spin-lattice relaxation times, and nuclear Overhauser enhancements requires that only one of the conformers thus predicted be, in fact, conformationally preferred in solution. These conformers are those predicted by hard-sphere exo-anomeric (HSEA) calculations.

Klaus Bock

Papers

Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Monosaccharides

A study of 13CH coupling constants in hexopyranoses

Carbon-13 nuclear magnetic resonance data for oligosaccharides

Further justification for the exo-anomeric effect. Conformational analysis based on nuclear magnetic resonance spectroscopy of oligosaccharides

Assignment of anomeric structure to carbohydrates through geminal13C-H coupling constants