Identification of the active-site serine in human pancreatic lipase by chemical modification with tetrahydrolipstatin

AbstractA chemical modification approach was used in this study to identify the active site serine residue of human pancreatic lipase. Purified human pancreatic lipase was covalently modified by incubation with [3H], [14C]tetrahydrolipstatin (THL), a potent inhibitor of pancreatic lipase. The radiolabeled lipase was digested with thermolysin, and the peptides were separated by HPLC. A single THL-peptide-adduct was obtained which was identical to that obtained earlier from porcine pancreatic lipase. This pentapeptide with the sequence VIGHS is covalently bound to a THL molecule via the side chain hydroxyl group of the serine unit corresponding to Ser-152 of the lipase. The selective cleavage of the THL-serine bond by mild acid treatment resulted in the formation of the δ-lactone Ro 40–444] in high yield and clearly proves that THL is attached via an ester bond and with retention of stereochemistry at all chiral centers to the side chain hydroxyl group of Ser-152 of the lipase. The results obtained for human pancreatic lipase corroborate the inhibition mechanism of THL found on the porcine enzyme, and are in full agreement with the identification of the Ser-152…His-263…Asp-176 catalytic triad in the X-ray structure of human pancreatic lipase

Chemical Information Media in the Chemistry Lecture Hall: A Comparative Assessment of Two Online Encyclopedias

The chemistry encyclopedia Römpp Online and the German universal encyclopedia Wikipedia were assessed by first-year university students on the basis of a set of 30 articles about chemical thermodynamics. Criteria with regard to both content and form were applied in the comparison; 619 ratings (48% participation rate) were returned. While both encyclopedias obtained very good marks and performed nearly equally with regard to their accuracy, the average overall mark for Wikipedia was better than for Römpp Online, which obtained lower marks with regard to completeness and length. Analysis of the results and participants' comments shows that students attach importance to completeness, length and comprehensibility rather than accuracy, and also attribute less value to the availability of sources which validate an encyclopedia article. Both encyclopedias can be promoted as a starting reference to access a topic in chemistry. However, it is recommended that instructors should insist that students do not rely solely on encyclopedia texts, but use and cite primary literature in their reports