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The present paper describes a spectroscopic method for determining the electron temperature T e and density N e in argon plasmas on the basis of a collisional-radiative model of argon. We measured T e and N e in a positive column of an argon dc discharge by the method developed, and compared them with those obtained by a Langmuir probe. The results for T e obtained by the spectroscopic method agreed roughly with those by the probe. However, a limitation of our method for obtaining N e was found.

The 1H NMR signals of the heme methyl, propionate and related chemical groups of cytochrome c3 from Desulfovibrio vulgaris Miyazaki F (D.v. MF) were site-specifically assigned by means of 1D NOE, 2D DQFCOSY and 2D TOCSY spectra. They were consistent with the site-specific assignments of the hemes with the highest and second-lowest redox potentials reported by Fan et al. (Biochemistry, 29 (1990) 2257-2263). The site-specific heme assignments were also supported by NOE between the methyl groups of these hemes and the side chain of Val18. All the results contradicted the heme assignments for D.v. MF cytochrome c3 made on the basis of electron spin resonance (Gayda et al. (1987) FEBS Lett., 217 57-61). Based on these assignments, the interaction of cytochrome c3 with D.v. MF ferredoxin I was investigated by NMR. The major interaction site of cytochrome c3 was identified as the heme with the highest redox potential, which is surrounded by the highest density of positive charges. The stoichiometry and association constant were two cytochrome c3 molecules per monomer of ferredoxin I and 10(8) M-2 (at 53 mM ionic strength and 25 degrees C), respectively.

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Site-specific heme assignment of the 'H-NMR spectrum of cytochrome c, of D. vulgaris Miyazaki F, a tetraheme protein, was established. The major reduction of the heme turned out to take place in the order of hemes I, III, IV and II (numbering in the crystal struceure). The hemes with the smallest and greatest solvent accessibility were reduced at the highest and lowest potentials on average, respectively. A cooperative interhems inteeaction was attributed to a pair of the closest hemes. namely, hemes III and IV. This assignment can provide the physicochemical basis for the elucidation of electron transfer of this protein. Cyeochrome c,; Tetraheme protein; Redox potentials of a tctraheme protein; 'H-NMR; Assignment of eedox potential