Resonance Raman spectra (RR) are reported for bovine adrenodoxin (Ado) and ferredoxin (Fd) from Porphyra umbilicalis, with 34S substituted at the bridging positions of the Fe2S2 cluster. All of the Fe-S stretching modes are assigned on the basis of the 34S isotope shifts and the previous analysis of analogue spectra. Appreciable frequency variations are seen, which can be explained on the basis of stronger Fe-S bonds, both bridging and terminal, in the proteins. This strengthening is attributable to protein compression effects or to H-bond interactions which reduced the negative charge on the iron-sulfur complex. In addition the Fe frequencies suggest an alteration in the Fe-S-C-C dihedral angles which induce mixing of the terminal Fe-S stretches with the S-C-C bending coordinate. The RR spectrum of the Porphyra umbilicalis Fd is identical with that of Fd isolated from Spirulina platensis, for which the crystal structure has been reported, as well as that of spinach Fd. RR spectra have also been obtained for a red paramagnetic protein (RPP) from Clostridium pasteurianum. Its frequencies suggest weakened Fe-S bridge bonding. RR spectra of reduced protein have been obtained for Ado and RPP, but not for Fd. The reduced protein spectra differ strongly from those of the oxidized proteins, and can be accounted for on the basis of a 30% reduction of the Fe-S force constants on the Fe11 side of the Fe2S2 cluster.

Steam gasification of chars from the pyrolysis of a Japanese bamboo and cedar was studied using a reactor that enabled experimental definition of the gas composition in the vicinity of gasifying char particles. Intraparticle diffusion of neither steam nor the product gases influenced the kinetics of gasification. The chars underwent noncatalytic and catalytic gasification in parallel. The noncatalytic gasification, in which kinetic parameters were successfully defined by those for the gasification of the acid-washed char, was first-order with respect to the amount of residual carbon over the entire range of char conversion. In consequence of this, contribution of the catalytic gasification was quantified as a function of the char conversion. Among the inherent alkali and alkaline earth metallic species, potassium (K) played the major catalytic role and its overall activity changed via a maximum in the course of gasification, suggesting the presence of optimum sizes of clusters or particles of K catalyst. The noncatalytic and catalytic reactions obeyed respective Langmuir−Hinshelwood mechanisms that involved inhibition by H2.

We reported evidence that horseradish peroxidase (HRP) and chloroperoxidase (CPO) catalyze oxygen transfer from H2O2 to thioanisoles [Kobayashi, S., Nakano, M., Goto, T., Kimura, T., & Schaap, A. P. (1986) Biochem. Biophys. Res. Commun. 135, 166-171]. In the present paper, the reaction mechanism of this oxygen transfer is discussed. The oxidation of para-substituted thioanisoles by HRP compound II showed a large negative rho value of -1.46 vs. the sigma + parameter in a Hammett plot. These results are in accord with the formation of a cation radical intermediate in the rate-determining step. Hammett treatments for HRP- and CPO-dependent S-oxygenations did not provide unequivocal proofs to judge the reaction mechanism, because of the poor correlations for sigma + and sigma p parameters. Different behavior was found in kinetics and stereoselectivity between the two enzymes. Results in the present study and recent studies strongly suggested the formation of a cation radical intermediate. The oxygen atom would transfer by reaction of compound II and the cation radical intermediate. Although involvement of the cation radical was not confirmed in the CPO system, a similar mechanism was proposed for CPO.

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Nascent volatiles from the pyrolysis of a type of woody biomass were reformed in a bed of charcoal at 750À850 °C. While the volatiles passed through the bed together with air at an air ratio of 0.115, the concentration of heavy tar (bp > 336 °C) decreased from 910 000 to 6À1020 mg/Nm 3 dry . This rapid and almost total decomposition of the tar can be ascribed to its deposition onto the charcoal surface, forming coke. The coke formation leads to the loss of the charcoal micropores that provide active sites. Therefore, simultaneous creation of micropores by gasification is necessary to maintain the charcoal activity. Steam played the role of gasifying agent, while O 2 was consumed mainly by gas-phase oxidation that supplied the heat for the reaction.

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The coordination structure of the ironsulfur complex in spinach ferredoxin and adrenodoxin is investigated by optical spectroscopy. The circular-dichroism and absorption spectra of these two-iron iron-sulfur proteins reveal weak electronic transitions in the nearinfrared wavelength range, 0.8-2.5 ,Am (12,500-4000 cm-l).On the basis of the low absorption intensities and large anisotropy factors, d d transitions of the iron can be identified in the reduced proteins at about 4000 cm-' and 6000 cm-. The low energy of these one-center ligand-field transitions, together with the similarity to the ligandfield spectrum of the one-iron protein rubredoxin, leads to the conclusion that the reduced two-iron iron-sulfur proteins also contain a high-spin ferrous ion in a distorted tetrahedral site.A currently attractive proposal for the structure of the active center of the two-iron iron-sulfur proteins such as the plant ferredoxins, adrenodoxin, and putidaredoxin, was put forth several years ago, in part to explain the absence of electron paramagnetic resonance (EPR) of the oxidized protein and the unusually low average g value observed upon one-electron reduction (4, 5). The proposed structure consists of a binuclear complex in which each iron atom is bonded to four sulfur atoms tetrahedrally disposed, as depicted schematically in Fig 1. Two sulfur atoms-the "acid-labile sulfides"-are common bridging ligands to the metal ions, while the four terminal mercaptide sulfur atoms are provided by the cysteinyl residues from the protein. It was further proposed (5) that the oxidized protein contains two high-spin ferric (d$, S = 5/2) ions antiferromagnetically coupled to give a net spin of zero in the ground state, while in the reduced protein a high-spin ferrous (d6, S = 2) ion is antiferromagnetically coupled to a high-spin ferric ion, resulting in a ground state with a net spin of 2. Recent reviews by Tsibris and Woody (6) and Palmer and Brintzinger (7) have discussed the chemical, magnetic resonance, magnetic susceptibility, and M6ss-bauer studies, which have all been consistent with this model, though no demonstration of the coordination geometry of the iron-sulfur complex was possible. The basis for investigating this and other aspects of the proposed structure by optical spectroscopy was recently developed by Eaton and Lovenberg, from their absorption and circular-dichroism studies in the near-infrared on the one-iron protein rubredoxin (8).Oxidized and reduced rubredoxin are known from x-ray diffraction (9), magnetic susceptibility (10), M6ssbauer (10), and optical studies (8) to contain a high-spin ferric and high-spin ferrous ion, repsectively, coordinated to four sulfurs of cysteinyl residues in an approximately tetrahedral complex (Fig. 1). The d -d electronic transitions of the tetrahedral ferrous ion, predicted from ligand-field theory to be characteristically very optically active, were found by Eaton and Lovenberg at about 6250 cm-' (1.6 jm) (8). In the absence of a very strong interaction between the irons,...

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