The structure provides insight into the pathogenic mechanisms of pertussis toxin and the evolution of bacterial toxins. Knowledge of the tertiary structure of the active site forms a rational basis for elimination of catalytic activity in recombinant molecules for vaccine use.

Reactions of H(2)O(2) with superoxide dismutase were studied by e.p.r. (electron paramagnetic resonance) spectroscopy and other methods. In agreement with earlier work, the Cu(2+) of the enzyme is reduced by H(2)O(2), although the reaction does not go to completion and its kinetics are not simple. With dilute enzyme the time for half-reduction with 9mm-H(2)O(2) is about 150ms. It is suggested that the reaction is a one-electron reduction, involving liberation of O(2) (-). On somewhat more prolonged exposure to H(2)O(2), the enzyme is inactivated. For enzyme in dilute solution and over a limited range of H(2)O(2) concentrations, inactivation is first-order with respect to enzyme and reagent, with k=3.1m(-1).s(-1) at 20-25 degrees C. Inactivation is accompanied by marked changes in the e.p.r. and visible spectra and appears to be associated with destruction of one histidine residue per subunit. It is suggested that this histidine is close to the metal in the native enzyme and essential for its enzymic activity.

Pertussis toxin is an exotoxin from the bacterium Bordetella pertussis which is important the pathogenesis of whooping cough and the generation of a protective immune response. The diverse biological activities of the toxin depend on its ability to recognize carbohydrate-containing receptors on a wide variety of eukaryotic cells. We present here the crystal structure of pertussis toxin complexed with a soluble oligosaccharide from transferrin. Binding sites for the terminal sialic acid-galactose moiety are revealed on both subunits S2 and S3 of the B-oligomer. Identification of amino acid residues involved in receptor binding will improve the design of genetically inactivated toxins for use in new acellular whooping cough vaccines.

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Cis and trans effects in six-coordinate cobalt(III) complexes have been observed1 mainly in studies of the thermodynamics and kinetics of replacement reactions. We have previously reported2-4 investigations by nmr spectroscopy of the cis effect in corrinoids,2 cobalt(III) dimethylglyoximates,3 and cobalt(III) Schiffs base complexes.4 However, chemical shifts are