David W. Cochran

Bio: David W. Cochran is an academic researcher from Indiana University. The author has contributed to research in topics: Nuclear magnetic resonance spectroscopy & Carbon-13. The author has an hindex of 15, co-authored 32 publications receiving 1268 citations.

Backbone dynamics of proteins as studied by 15N inverse detected heteronuclear NMR spectroscopy: application to staphylococcal nuclease.

Abstract: This paper describes the use of novel two-dimensional nuclear magnetic resonance (NMR) pulse sequences to provide insight into protein dynamics. The sequences developed permit the measurement of the relaxation properties of individual nuclei in macromolecules, thereby providing a powerful experimental approach to the study of local protein mobility. For isotopically labeled macromolecules, the sequences enable measurements of heteronuclear nuclear Overhauser effects (NOE) and spin-lattice (T1) and spin-spin (T2) 15N or 13C relaxation times with a sensitivity similar to those of many homonuclear 1H experiments. Because T1 values and heteronuclear NOEs are sensitive to high-frequency motions (10(8)-10(12) s-1) while T2 values are also a function of much slower processes, it is possible to explore dynamic events occurring over a large time scale. We have applied these techniques to investigate the backbone dynamics of the protein staphylococcal nuclease (S. Nase) complexed with thymidine 3',5'-bisphosphate (pdTp) and Ca2+ and labeled uniformly with 15N. T1, T2, and NOE values were obtained for over 100 assigned backbone amide nitrogens in the protein. Values of the order parameter (S), characterizing the extent of rapid 1H-15N bond motions, have been determined. These results suggest that there is no correlation between these rapid small amplitude motions and secondary structure for S. Nase. In contrast, 15N line widths suggest a possible correlation between secondary structure and motions on the millisecond time scale. In particular, the loop region between residues 42 and 56 appears to be considerably more flexible on this slow time scale than the rest of the protein.

Amiloride: a molecular probe of sodium transport in tissues and cells

Abstract: The potassium-sparing diuretic amiloride has proven to be a useful pharmacological tool for elucidating the molecular basis and physiological regulation of facilitated sodium entry in tissues and cells. There are two general classes of Na+ transport mechanisms which are sensitive to this drug: 1) a conductive Na+ entry pathway found in electrically high resistance epithelia and 2) a Na+-H+ electroneutral exchange system found in certain leaky epithelia such as the renal proximal tubule. This latter system is also found in many different cellular preparations and seems to function in cell proliferation and differentiation, volume regulation, and intracellular pH regulation. In these cells, this exchange pathway becomes operational usually after some external stimuli. Much higher concentrations of amiloride are required to inhibit the exchange pathway than those required to inhibit the Na+ entry pathway. This drug is the most potent and specific inhibitor of Na+ entry found to date and thus affords the opportunity to be used as a label for the isolation of these transport moieties.

Carbon-13 NMR spectroscopy

Abstract: Features in this edition are references (over 1,000), profuse illustration, a discussion of modern pulse techniques for spectral analysis, and extensive and thorough cataloguing of chemical shift data (over 200 pages) in readily accessible form. An attractive feature is the use of structural formulae with shifts inscribed in the structure. This new edition has been completely revised to take into account new techniques and the increased use of computers. The new methods described include those for multiplicity analysis and two-dimensional homo- or hetero-nuclear shift correlations. New sections about coupling constants, organophosphorus and organometalic compounds as well as synthetic polymers have been added. As in the second edition, the authors survey the large number of /sup 13/C NMR applications to organic molecule and natural products in a representative and systematic rather than an exhaustive way.

Synthesis of Pyridine and Dihydropyridine Derivatives by Regio- and Stereoselective Addition to N-Activated Pyridines

Abstract: Stereoselective Addition to N-Activated Pyridines James A. Bull,‡ James J. Mousseau, Guillaume Pelletier,† and Andre ́ B. Charette*,† †Department of Chemistry, Universite ́ de Montreál, P.O. Box 6128, Station Downtown, Montreál, Queb́ec, Canada H3C 3J7 ‡Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K. Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

The chemistry and biological significance of saponins in foods and feedingstuffs.

Abstract: Saponins occur widely in plant species and exhibit a range of biological properties, both beneficial and deleterious. This review, which covers the literature to mid 1986, is concerned with their occurrence in plants and their effects when consumed by animals and man. After a short discussion on the nature, occurrence, and biosynthesis of saponins, during which the distinction between steroidal and triterpenoid saponins is made, the structures of saponins which have been identified in a variety of plants used as human foods, animal feedingstuffs, herbs, and flavorings are described. Many of these compounds have been characterized only during the last 2 decades, and modern techniques of isolation, purification, and structural elucidation are discussed. Particular consideration is given to mild chemical and enzymatic methods of hydrolysis and to recent developments in the application of NMR and soft ionization MS techniques to structural elucidation. Methods currently used for the quantitative analysis of saponins, sapogenols, and glycoalkaloids are critically considered; advances in the use of newer methods being emphasized. The levels of saponins in a variety of foods and food plants are discussed in the context of the methods used and factors affecting these levels, including genetic origin, agronomic, and processing variables, are indicated. Critical consideration is given to the biological effects of saponins in food which are very varied and dependent upon both the amount and chemical structure of the individual compounds. The properties considered include membranolytic effects, toxic and fungitoxic effects, adverse effects on animal growth and performance, and the important hypocholesterolemic effect. A final section deals briefly with the pharmacological effects of saponins from ginseng, since use of this plant is increasing in certain sections of western society as well as being traditional in the Orient.