Cytochrome c4 is a 190-residue protein active in the aerobic and anaerobic respiration of several bacteria. We have isolated Pseudomonas stutzeri (ATCC no. 11607) cytochrome c, by an optimized growth procedure following factorial design. The ultravioletlvisible spectra of reduced cytochrome c4 have a composite alp band which can be resolved into six components. One of these seems to be specific for the high-potential heme group. The kinetics for full oxidation and reduction with the two inorganic redox couples, [C~(terpy)~]*+'~+ and [C~(bipy),]~'/~+, is formally compatible with either bi-or tri-exponential kinetics. The former would be in line with weak interaction between the heme groups, the latter with notable interaction effects. Arguments in favour of the latter and a cooperative two-electron transfer pattern are given. All phases are approximately proportional to the Co-complex concentration, implying that intramolecular electron transfer in this time range is unlikely. The rate constants are in the range (0.7-80)X104 M-' s-' at pH = 7.6 (Tris) and 0.1 M NaCl and very little dependent on the ionic strength in the range 0.1-0.3 M. The reduction potentials could be calculated from the forward and reverse rate constant ratios. The values are 241 ? 5 and 328 -f 2 mV (Nernst hydrogen electrode) if bi-exponential kinetics is used and interaction between the heme groups disregarded. The intrinsic microscopic reduction potential values are closer when the tri-exponential, cooperative model is used as this model transfers 30-40 mV to electrostatically dominated interaction potentials. The overall electron transfer pattern can be related to the recently determined crystal structure of the F! stutzeri cytochrome c,.Keywords. Electron transfer; cytochrome c4 ; bandshape resolution ; cooperativity.Multi-centre metalloproteins or protein complexes are a dominating feature in respiratory and photosynthetic electron transfer (ET) 11-41. One functional implication of this is that close and specific mutual orientation of individual metallic ET centres ensures facile long-range directional ET by favourable electronic coupling [3]. In addition, electric field changes associated with a given ET step may induce electrostatic or conformational changes in other centres, poising the latter for favourable subsequent ET in a cooperative multi-centre ET pattern [5-91. Long-range ET features relating to the donor-acceptor electronic coupling and energy gap have been broadly investigated [3, 4, 10-141. Well characterized cases of multicentre ET cooperativity are much more limited and probably restricted to the four-heme cytochromes (cyts) c,. These have been functionally mapped in great detail 15-8, 15, 161 and elements of a theoretical ET frame suggested [9]. Two-centre proteins offer attractive alternatives towards cooperative ET mapping due to the much smaller number of interactions. Compared with fourcentre proteins, the maximum number of microscopic reduction potentials is thus reduced from 32 to four and the number of rate cons...

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Lipases can catalyze halogenations (see scheme for an example) under the same experimental conditions as "metal-free haloperoxidases". This activity should, therefore, not be attributed to a new unique class of enzymes, or even to metal-free haloperoxidases, but should rather be regarded as a side activity of well-known hydrolases.

The chemical composition of the surface of an amphiphilic diblock copolymer film, comprised of polystyrene and poly(4-(2-(2-(2-acetoxy)ethoxy)ethoxy)styrene), has been characterized upon equilibration in water and in a vacuum, employing surface sensitive near-edge X-ray absorption fine structure spectroscopy. The outermost surface layer exhibits a reversible exchange between the hydrophilic and hydrophobic polymer segments as the equilibrating interface is changed between water and vacuum, respectively. Surprisingly, time-dependent measurements show that a substantial partial molecular reorganization toward a vacuum-equilibrated surface occurs already at 60 °C, which is significantly below the glass transition temperature of the polystyrene block.