Methane Emission from Enteric Fermentation: Methanogenesis and Fermentation

Rumen fermentation of carbohydrates plays a fundamental role in ruminant metabolism as the main source of energy. Acetic, propionic and butyric acids (namely, volatile fatty acids, VFA) are the main products of the rumen fermentation of structural and nonstructural carbohydrates con- tained in the ruminant’s diet. The metabolic pathways involved in VFA production are strictly linked to methane emission, because hydrogen is actively produced during the fermentation of structural carbohydrates, and it is rapidly metabolised by methanogens, in order to maintain the optimal thermodynamic condition for the metabolism of the microbe consortium in the rumen. Hydrogen plays also a fundamental role in the maintenance of the equilibrium among VFA pathways and in their interconversion. In this chapter, after a brief chemical description of dietary carbohydrates, individual VFA pathways are described in order to put in evidence the thermodynamic control points of each pathway and the production of energy and reductive equivalent. Then, the relationship between hydrogen, VFA and methane production has been reviewed, considering the role of some dietary factors, the substrate competition between different meta- bolic pathways and the models of VFA estimation

Salt dependence of an α-helical peptide folding energy landscapes

We used CD,UV resonance Raman spectroscopy, and molecular dynamics simulation to examine the impact of salts on the conformational equilibria and the Ramachandran Ψ angle (un)folding Gibbs free energy landscape coordinate of a mainly polyalanine α-helical peptide, AP of sequence AAAAA-(AAARA)3A. NaClO4 stabilizes α-helical-like conformations more than does NaCl, which stabilizes more than Na 2SO4 at identical ionic strengths. This α-helix stabilization ordering is the reverse of the Hofmeister series of anions in their ability to disorder water hydrogen bonding. Much of the NaClO4 α-helix stabilization results from ClO4- association with the AP terminal-NH3+ groups and Arg side chains. ClO4- stabilizes 310-helix conformations but destabilizes turn conformations. The decreased Cl- and SO 42- AP α-helix stabilization probably results from a decreased association with the Arg and terminal -NH3+ groups. Cl- is expected to have a smaller binding affinity and thus stabilizes α-helical conformations intermediately between NaClO 4 and Na2SO4. Electrostatic screening stabilizes π-bulge conformations. © 2009 American Chemical Society