ShK toxin, a 35-residue peptide isolated from the Caribbean sea anemone Stichodactyla helianthus, is a potent inhibitor of the Kv1.3 potassium channel in lymphocytes. The natural toxin contains three disulfide bonds. The disulfide pairings of the synthetic ShK toxin were elucidated as a prerequisite for studies on its structure-function relationships. The toxin was fragmented at pH 6.5 using either thermolysin or a mixture of trypsin and chymotrypsin followed by thermolysin. The fragments were isolated by RP-HPLC and were identified by sequence analysis and MALDI-TOF mass spectrometry. The three disulfides were unambiguously identified in either proteolytic digest: Cys 3 to Cys 35, Cys ~2 to Cys 28 and Cys 17 to Cys 32. The CysLCys 35 disulfide, linking the aminoand carboxyl-termini, defines the characteristic cyclic structure of the molecule. A similar disulfide pairing motif is found in the snake venom-derived potassium channel blocker dendrotoxin and the mammalian antibiotic peptide defensins.

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Abstract. In micellar electrokinetic capillary chromatography (MECC) the most widely used surfactant for the pseudostationary phase is sodium dodecyl sulfate (SDS), although other types of surfactants have been investigated. We have synthesized the magnesium salt of dodecyl sulfate (Mg(DSM in order to investigate how changes in the counter ion identity affect resolution via changes in selectivity (a) and retention. Buffer solutions containing Mg(DS), exhibited operating currents and electroosmotic velocities one third to one half that of a comparable SDS buffer solution, and significantly larger methylene and functional group selectivities for the compounds studied. In addition, capacity factors, k', for neutral solutes were between 1.5 and 2.5 times larger for the Mg(DS),. The elution range, hc/to, for the Mg(DS), was independent of the percentage of organic modifier in the buffer solution while the elution range for SDS increased as the percentage of organic modifier increased. Improvements in a and increased retention resulted in increased Rs for neutral solutes in Mg(DS)2. The relatively constant elution range for Mg(DS), also aided in the retention-mediated optimization of R, and R, per unit time.

Abstract. Various tetraalkylammonium ions, such as tetramethyl-, tetrapropyl-, tetrapentyl-, and cetyltrimethylammonium, can be added to sodium dodecyl sulfate (SDS) micellar solutions to achieve unique selectivities in micellar electrokinetic chromatography (MEKC). The cetyltrimethylammonium/SDS buffer system showed the greatest increase in methylene selectivity, while both tetrapropylammonium/SDS and cetyltrimethylammoniumlSDS buffer systems had the greatest selectivities for the solutes studied. In addition, the buffer systems that used symmetrical tetraalkylammonium ions showed reductions in retention specific for the carbonyl functional group. The tetramethylammonium/SDS buffer system had the best resolution due to both improved selectivity and an elution range that was 2.5 times that of a comparable SDS buffer system.