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The enzymatic activity of phenoloxidase is assayed routinely in the presence of SDS. Similar assay conditions elicit phenoloxidase activity in another type 3 copper protein, namely hemocyanin, which normally functions as an oxygen carrier. The nature of the conformational changes induced in type 3 copper proteins by the denaturant SDS is unknown. This comparative study demonstrates that arthropod hemocyanins can be converted from being an oxygen carrier to a form which exhibits phenoloxidase activity by incubation with SDS, with accompanying changes in secondary and tertiary structure. Structural characterisation, using various biophysical methods, suggests that the micellar form of SDS is required to induce optimal conformational transitions in the protein which may result in opening a channel to the di-copper centre allowing bulky phenolic substrates access to the catalytic site.

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The dienyl cluster compounds [M,H(CO),(p,-o:q2:q2-C6H7)] ( M = Ru or 0 s ) have been synthesised from [Os,H,(CO),,] or [M,(CO),,(MeCN),] ( M = R u or 0 s ) with cyciohexa-1.3-diene. The molecular and crystal structure of [ Ru,H (CO),(C,H,)] has been established by single-crystal X-ray diffraction analysis: monoclinic, space group P2,, a = 8.487(6), b = 12.031 (3). c = 9.073(2) A, p = 92.43(4)' and Z = 2. The cyclohexadienyi ligand is involved in one CJ and two 7c interactions with the metal triangle, while the H (hydride) ligand bridges the long Ru-Ru bond [3.052( 1 ) A]. The other two Ru-Ru bond lengths are the same [2.837(1) A] and comparable to those observed in [Ru,(CO),(~,-q2:q2:qz-C,H,)I. The H( hydride) position afforded by the diffraction experiment has been compared with the result of potentialenergy minimization procedures. The molecular organization within the lattice has been explored by means