Cyclic hexapeptides related to somatostatin Conformational analysis employing 1H-NMR and molecular dynamics

We report the conformational analysis of a series of cyclic hexapeptides related to the hormone somatostatin utilizing ¹H NMR spectroscopy and NOE restrained molecular dynamics. The conformational preferences and results from biological analysis of these analogs (previous paper) allow for refinement of the current understanding of the structure-activity relationship of somatostatin. For most of the molecules examined, a βII′ turn about the d -tryptophan-lysine residues, postulated to be required for biological activity, was present. From the NOE restrained molecular dynamics, it can be seen that the turn structure is important for the maintenance of the proper orientation of the side chains of the adjacent phenylalanine, tryptophan and lysine. The biologically active analogs have the side chains of lysine and d -tryptophan extended away from the 18-membered ring in close proximity to each other for a significant portion of the dynamic simulations. Although other conformations are accessible and monitored during the simulations, we believe this is important for biological recognition. The absence of the βII′ turn at the d -tryptophan-lysine disrupts this side chain array producing inactive molecules. The role of the bridging region, the Phe-Pro dipeptide, is to stabilize the βII′ turn and help maintain the proper orientation of the biologically important side chains.     

Bedside Recordings of His-Bundle Electrograms Using Conventional Twelve-Lead Surface Electrocardiography

Bedside Recording of His Potentials. Introduction: Endocavitary His-bundle electro-grams are usually recorded using high fidelity amplifiers and special filters.
Methods and Results: To evaluate whether similar recordings could be obtained using a 12-lead surface electrocardiograph, we compared recordings obtained during an electrophysiologic study in 33 patients to those obtained by connecting the two poles of the bipolar catheter, used during the study as the His catheter, to the right and left arm leads of the surface electrocardiograph. We recorded His-bundle electrograms using both techniques in all patients. There were no differences in measurements obtained between the two techniques.
Conclusion: His-bundle electrograms can be recorded reliably with a conventional electro-gram without sophisticated systems.