Catalytic Mechanism of the Metal-Free Hydrogenase from Methanogenic Archaea: Reversed Stereospecificity of the Catalytic and Noncatalytic Reaction.

By activation of the hydrogen acceptor, the metal-free hydrogenase from methanogenic archaea catalyzes the reduction of methenyl tetrahydromethanopterin with H . According to NMR spectroscopic analysis of the conformation of the hydrogen acceptor in solution and of the stereospecificity of the catalyzed and noncatalyzed reaction, in the enzyme-catalyzed reaction the hydrogenation product is formed in a constraint conformation which relaxes upon dissociation from the enzyme. This exergonic conformational change could help to avoid product inhibition of the enzyme.

SIAM, a Novel NMR Experiment for the Determination of Homonuclear Coupling Constants.

The simultaneous acquisition of in-phase and antiphase multiplets with high sensitivity and minimum overlap (see section of 2D spectra on the right) is possible in a novel NMR experiment. Based on this method, homonuclear coupling constants such as the J(H ,H ) couplings in peptides and proteins can be determined quantitatively without isotope labeling.