We have studied binding and block of sodium channels by 12 derivatives of the 22-residue peptide mu-conotoxin GIIIA (mu-CTX) in which single amino acids were substituted as follows: Arg or Lys by Gln, Gln-18 by Lys, Asp by Asn, and HO-Pro by Pro. Derivatives were synthesized as described by Becker et al. [(1989) Eur. J. Biochem. 185, 79]. Binding was measured by displacement of labeled saxitoxin from eel electroplax membranes (100 mM choline chloride, 10 mM HEPES-NaOH, pH 7.4). Blocking kinetics were evaluated from steady-state, single-channel recordings from rat skeletal muscle sodium channels incorporated into planar, neutral phospholipid/decane bilayers (200 mM NaCl, 10 mM HEPES-NaOH, pH 7.0). Blocking events generally appeared as periods of seconds to minutes in which current through the single channel was completely eliminated. A notable exception was seen for the substitution Arg-13-Gln for which the "blocked" events showed measurable conductances of about 20-40% of the open state. The substitution of Arg-13 reduced binding to electroplax membranes to undetectable levels and increased the apparent dissociation constant determined for skeletal muscle channels by greater than 80-fold compared with the native peptide. Other substitutions caused smaller decreases in affinity. The decreased potency of the toxin derivatives resulted both from increases in the rates of dissociation from the channel, and from decreases in association rates. Our data support the suggestion by Sato et al. [(1991) J. Biol. Chem. 265, 16989] that Arg-13 associates intimately with the binding site on the channel. In addition, our results suggest that certain residues affect almost exclusively the approach and docking of the toxin with its binding site, others appear to be important only to the strength of the association once binding has taken place, and yet others affect both.

Few experimental data illuminate the relationship between the molecular structures that mediate ion conduction through voltage-dependent ion channels and the structures responsible for sensing transmembrane voltage and controlling gating. To fill this void, we have used a strongly cationic, mutated mu-conotoxin peptide, which only partially blocks current through voltage-dependent sodium channels, to study voltage-dependent activation gating in both bound and unbound channels. When the peptide binds to the ion-conducting pore, it inhibit channel opening, necessitating stronger depolarization for channel activation. We show that this activation shift could result entirely from electrostatic inhibition of the movement of the voltage-sensing S4 charges and estimate the approximate physical distance through which the S4 charges move.

The presence of aluminum in a minimal mineral medium, with citrate as the sole source of carbon, elicited the production of an exocellular lipid‐rich residue in Pseudomonas fluorescens. Although aluminum affected the growth rate, no apparent diminution in cellular yield was observed in medium supplemented with up to 3 mM of the trivalent metal. While a 10% reduction in cellular yield was recorded in medium with 7.5 mM aluminum, a decrease of 69% was reported in medium supplemented with 50 mM aluminum at stationary phase of growth. The wet weight of the pellet ranged from 5.9 to 70.3 mg mL−1 of culture in medium supplemented with 1–30 mM aluminum. The trivalent metal was immobilized in this precipitate and associated with phosphate moieties. Both neutral lipids and phospholipids constituted the pellet. More than 90% of the weight of the wet pellet was lost following lyophilization. The percentage of aluminum immobilized increased with the concentration of trivalent metal in the medium. Preconditioned cells showed an improved growth rate, and the cellular yield was slightly higher than for unadapted cells.

This book is the edited proceedings of the 8th International Symposium on Ceramics in Medicine, held in Florida in November 1995. This work contains the latest research on the increasingly important and wide-ranging role of bioceramics in medicine. This volume will be a vital reference document for academic and industrial researchers in the field, and it will also be of great value to students and lecturers in materials science, medical engineering, and clinical implantology. There are 85 papers divided into the following sections: Bone Biology, Spinal Reconstruction, Orthopaedic Applications, ENT and Maxillofacial, Dental Applications, Calcium Phosphate Coatings, New Directions, Composites, and Bioactive Glasses. There are an author index and a subject index. JA965604A S0002-7863(96)05604-1 Concepts in Chemistry: A Contemporary Challenge. Edited by Dennis H. Rouvray (University of Georgia). Wiley: New York. 1997. xvi + 420 pp. $79.95. ISBN 0-471-96555-3.This volume of twelve essay reviews is largely based on lectures originally presented as part of the conference Are the Concepts of Chemistry all Fuzzy?, held in Pitlochry, Scotland, in July of 1995, and organized by Dennis Rouvray and Edward Kirby under the sponsorship of the International Society for Mathematical Chemistry. The range of topics includes the fuzziness of chemical concepts; the role of mathematics in chemistry; the concepts of periodicity and hyperperiodicity; the concept of chemical structure; electron-counting rules and topology in carbon allotropes, inorganic clusters, and superconductors (three essays); the concept of ring currents; the concepts of symmetry and chirality (two essays); the concept of complexity; and the concept of epitopes and paratopes in immunological reactions.In keeping with both the title of the original conference and the editor's comments in the preface, one might expect each essay to focus on an analysis of the "fuzziness" of a key chemical concept using the paradigm of fuzzy logic theory. However, as is usually the case with volumes based on symposia, the various authors often wander far from the organizers' original intention. Indeed, a measure of just how much wandering has occurred can be gaged from the fact that the term "fuzzy" and its various derivatives (fuzzified, fuzziness, etc.) appear only 13 times in the index, and that nine of these references are to the editor's own paper.In any analysis of the precision or fuzziness of a concept, one would reasonably expect the author to trace the history of the concept, documenting both its origins and historical permutations; to document the extent of its current fuzziness by citing examples of variable usage in the modern literature; to cite specific examples in which application of the concept leads to ambiguity; and, lastly, to suggest ways of making its meaning more precise. All of this assumes, of course, that the author has selected an important general chemical concept for analysis in the first place. Very few of the essays in this volume meet all five of these ...