T Wessels | PubMed Health

PubMed1999

Single-crystal-like diffraction data from polycrystalline materials

A method for solving structures from powder diffraction data was developed, and its validity was demonstrated on three complex structures. The method uses a textured sample and exploits the high intensity and parallel nature of synchrotron radiation. In principle, crystal structures as complex as those routinely solved by single-crystal methods can be determined with this approach. For example, the as-synthesized form of the zeolite UTD-1, with 69 nonhydrogen atoms in the asymmetric unit, could be solved directly. With this method, a larger range of structural complexity becomes accessible to scientists interested in the structures of polycrystalline materials that cannot be grown as single crystals.

Journal Article↗

PubMed1994

Evidences for physically different catalytic and regulatory nucleotide binding sites on the chloroplast H(+)-ATPase.

Chloroplast thylakoids which were incubated with pyridoxal-5-phosphate (PLP) in the dark, exhibit a slower ADP-binding curve in the light and lack the rapid initial phase of rebinding of loosely bound nucleotides upon de-energetization. The [14C]NBD binding pattern in subunits of PLP-modified thylakoids is reduced to that one found if ADP was present in the modification step. The [14C]NBD binding pattern in subunits of activated and successive PLP-modified CF1 is reduced to that one found in the latent enzyme. As in the latent (not activated) ATPase Lys beta 359 is modified by PLP, we conclude that this amino acid residue belongs to a regulatory binding site which binds ADP tightly upon de-energetization and releases it upon energetization. In the activated enzyme, however, the modified residue is related to a 9 kDa peptide in beta, which contains the conserved lysine 178. This site is proposed to be a catalytic one.

Adenosine Diphosphate↗