Gastrin stimulates the production of Reg protein in gastric ECL cells, which may be involved in the gastrin-induced gastric mucosal cell growth.

Mastoparan-X, a tetradecapeptide from wasp venom, has been proposed to cause secretion from various kinds of cells by the direct activation of GTP-binding regulatory proteins (G proteins) that couple to phospholipase C. The mechanism of the activation has been shown to be very similar to that of G-protein-coupled receptors in vitro, and the interaction with membranes seems to be very important for the activation of G proteins that are membrane-bound [Higashijima, T., Uzu, S., Nakajima, T., & Ross, E. M. (1988) J. Biol. Chem. 263, 6491-6494]. We report here the precise vesicle-bound conformation of mastoparan-X in the presence of perdeuterated phospholipid vesicles, determined by two-dimensional 1H-NMR analyses of transferred nuclear Overhauser effects, combined with distance geometry and molecular dynamics calculations. Of 14 amino acid residues, the C-terminal 12 residues take an alpha-helical conformation upon binding to the phospholipid bilayer. The overall structure of the alpha-helix is amphiphilic, with three lysine side chains located on one side and with hydrophobic side chains on the other side. This conformation of mastoparan-X was maintained both in the gel and in the liquid-crystalline phases of the membranes. The conformation described herein will provide a useful basis for understanding conformation-activity relationships of mastoparan analogs as activators of G proteins. These studies will help to design novel potent analogs for the regulation of G proteins and to analyze receptor-G-protein interactions.

Abstract-We studied numerous specimens of the Norton County enstatite achondrite (aubrite) by optical microscopy, electron microprobe, and neutron-activation analysis. Our main conclusions are the following: 1. Norton County is a fragmental impact breccia, consisting of a clastic matrix made mostly of crushed enstatite, into which are embedded a variety of mineral and lithic clasts of both igneous and impact melt origin. 2. The Norton County precursor materials were igneous rocks, mostly plutonic orthopyroxenites, not grains formed by condensation from the solar nebula. 3. The Mg-silicate-rich aubrite parent body experienced extensive melting and igneous differentiation, causing formation of diverse lithologies, some of which have not been described previously. These lithologies include dunites (represented by forsterite crystals), plutonic orthopyroxenites (represented by most enstatite crystals in the matrix), plutonic pyroxenites (the pyroxenitic clasts), and plagioclase-silica rocks (like the feldspathic clasts). Presence of impact melt breccias (the microporphyritic clasts and the diopside-plagioclase-silica clast) of still different compositions further attest to the lithologic diversity of the aubrite parent body.

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