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Triclosan, a common antibacterial additive used in consumer products, is an inhibitor of FabI, the enoyl reductase enzyme from type II bacterial fatty acid biosynthesis. In agreement with previous studies [Ward, W. H., Holdgate, G. A., Rowsell, S., McLean, E. G., Pauptit, R. A., Clayton, E., Nichols, W. W., Colls, J. G., Minshull, C. A., Jude, D. A., Mistry, A., Timms, D., Camble, R., Hales, N. J., Britton, C. J., and Taylor, I. W. (1999) Biochemistry 38, 12514-12525], we report here that triclosan is a slow, reversible, tight binding inhibitor of the FabI from Escherichia coli. Triclosan binds preferentially to the E.NAD(+) form of the wild-type enzyme with a K(1) value of 23 pM. In agreement with genetic selection experiments [McMurry, L. M., Oethinger, M., and Levy, S. B. (1998) Nature 394, 531-532], the affinity of triclosan for the FabI mutants G93V, M159T, and F203L is substantially reduced, binding preferentially to the E.NAD(+) forms of G93V, M159T, and F203L with K(1) values of 0.2 microM, 4 nM, and 0.9 nM, respectively. Triclosan binding to the E.NADH form of F203L can also be detected and is defined by a K(2) value of 51 nM. We have also characterized the Y156F and A197M mutants to compare and contrast the binding of triclosan to InhA, the homologous enoyl reductase from Mycobacterium tuberculosis. As observed for InhA, Y156F FabI has a decreased affinity for triclosan and the inhibitor binds to both E.NAD(+) and E.NADH forms of the enzyme with K(1) and K(2) values of 3 and 30 nM, respectively. The replacement of A197 with Met has no impact on triclosan affinity, indicating that differences in the sequence of the conserved active site loop cannot explain the 10000-fold difference in affinities of FabI and InhA for triclosan.

On Methuselah's Trail: Living Fossils and the Great Extinctions. ByPeter Douglas Ward. W. H. Freeman: 1991. Pp.214. $18.95, £14.95.

Panel on Physical Properties of Propellants, Solid Propellant Information Agency PP12 (June 1959). 8 Smith, T. L., "Stress-strain-time-temperature relationships for polymers," American Society for Testing Materials Special Tech. Publ. 325 (1962). 9 Smith, T. L., "Ultimate tensile properties of elastomers. I. Characterization by a time and temperature independent failure envelope," J. Poly Sci. AI, 3597-3615 (1963). 10 Rose, EL, letter to the editor of Engineering (British) 148,536 (November 10,1939). 11 Ward, W. H., letter to the editor of Engineering (British) 148, 698 (December 22,1939). 12 Carman, P. C., Flow of Gases Through Porous Media (Butterworths Scientific Publications Ltd., London, 1956), p. 8. 13 Graton, L. C. and Frazer, H. J., "Systematic packing of spheres—with particular relation to porosity and permeability," J. Geol. 45, 785-909 (1935). 14 Brown, L. S. and Pierson, C. U., "Linear traverse technique for measurement of air in hardened concrete," J. Am. Concrete Inst., 117-123 (October 1950). 15 Ailing, H. L. and Valentine, W. G., "Microscopic rock analysis," Am. J. Sci. XIV, 50-65 (July 1927). 16 Capener, E. L., personal communication (January 1965). 17 Handbook of Chemical Microscopy, Chamot, E. M. and Mason, C. W. (John Wiley & Sons, Inc., New York, 1958), Vol. 1, pp. 483-488.

The areaa-atrain behaviors of wool fibers varying in cross-sectional area are cal culated theoretically and the predicted effects verified experimentally. Calculation of the uniform fiber curve has been carried out and values are obtained for the curve parameters for a range of cross-sectional area variability. Besides this type of dimensional irregularity, structural variations occur in wool fibers and these can considerably influence stress-strain behavior. A knowledge of the relationship between structural variability and stress-strain behavior can be used to test the adequacy of the various models which have been proposed to explain the mechanical hehavior of wool fibers. 'rhis has been achieved by predicting the stress-strain behavior that might be expected from fibers with varying structural compositions and comparing the results with actual stress-strain behavior variations (after removing any effects due to cross-sectional area variability). 1. Collins, J. D., J. Sci. Instr.40, 198-199, 1963. 2. Collins, J. D., Ph.D. Thesis, University of N.S.W., Australia, 1964. 3. Collins, J. D. and Chaikin, M., Proceedings of the 3rd International Wool Textile Research Confer ence, Paris, 1965. 4. Dusenbury, J. H. and Wakelin, J. H., Textile Res. J.28, 989-1005, 1958. 5. Evans, T. F. and Montgomery, D. J., Textile Res. J.23, 689-701, 1953. 6. Feughelman, M., Textile Res. J.29, 223-228, 1959. 7. Feughelman, M. and Haly, A. R., Colloque, "Struc ture de la Laine," Paris, 159-183, 1961. 8. Feughelman, M. and Lunney, H. W., Wool Sci. Rev.21, 25, 1962. 9. Feughelman, M., Textile Res. J.33, 1013-1022. 1963. 10. Kenny, P. and Chaikin, M., J. Text. Inst.50, T18- 38. 1959. 11. Lindberg, J., Textile Res. J.23, 683-689, 1953. 12. Lundgren, H. P. and Ward, W. H., "Ultrastructure of Protein Fibres," edited by R. Borasky, printed in U.S.A. by Academic Press, New York and Lon don, 1963, Page 64. 13. Meredith, R., J. Textile Inst.36, T107-130, 1945. 14. Munakata, H., Textile Res. J.34, 97-109, 1964. 15. Rigby, B. J., Textile Res. J.32, 1034-1035, 1962. 16. Schiefer, H. F., Fourt, L., and Krofp, R. T., Tex tile Res. J.17, 689-713, 1947. 17. Skertchly, A. R. B., J. Textile Inst.55, T154-161. 1964. 18. Skertchly. A. R. B., Nature202, 161-164, 1964. 19. Turner. J. D. and Woods. H. J., Colloque, "Struc ture de la Laine," 19-24, Paris, 1961.