No abstract

The local adsorption structure of PF3 on Ni(111) has been investigated using a combination of P K-edge near-edge and surface extended X-ray absorption fine structure (NEXAFS and SEXAFS) and normal incidence standing X-ray wavefield absorption (NISXW) at both the P and F atoms in order to determine the adsorption site, the adsorbate-substrate bond-length, the molecular orientation and the internal structure of the adsorbed species. The molecule is found to be adsorbed atop a top layer Ni atom at a P-Ni nearest-neighbour distance of 2.07+or-0.03 AA, with its C3v symmetry axis perpendicular to the surface, and with an internal structure (both bond-lengths and bond angles) unchanged from that of the free molecule. The results also indicate that there is no change in the Ni(111) substrate structure induced by the adsorption, and the PF3 has a much larger vibrational amplitude parallel to the surface than perpendicular to the surface, presumably associated with a Ni-PF3 wagging mode.

The use of a microsomal preparation from skeletal muscle revealed that both Ca(2+) transport and Ca(2+)-dependent ATP hydrolysis linked to Sarco-Endoplasmic Reticulum Ca(2+)-ATPase are inhibited by epigallocatechin-3-gallate (EGCG). A half-maximal effect was achieved at approx. 12 μM. The presence of the galloyl group was essential for the inhibitory effect of the catechin. The relative inhibition of the Ca(2+)-ATPase activity decreased when the Ca(2+) concentration was raised but not when the ATP concentration was elevated. Data on the catalytic cycle indicated inhibition of maximal Ca(2+) binding and a decrease in Ca(2+) binding affinity when measured in the absence of ATP. Moreover, the addition of ATP to samples in the presence of EGCG and Ca(2+) led to an early increase in phosphoenzyme followed by a time-dependent decay that was faster when the drug concentration was raised. However, phosphorylation following the addition of ATP plus Ca(2+) led to a slow rate of phosphoenzyme accumulation that was also dependent on EGCG concentration. The results are consistent with retention of the transporter conformation in the Ca(2+)-free state, thus impeding Ca(2+) binding and therefore the subsequent steps when ATP is added to trigger the Ca(2+) transport process. Furthermore, phosphorylation by inorganic phosphate in the absence of Ca(2+) was partially inhibited by EGCG, suggesting alteration of the native Ca(2+)-free conformation at the catalytic site.