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Presents an overview of the rapidly developing field of sulfur biochemistry. Role of sulfur in biological systems; Occurrence of sulfur in inorganic systems; Iron-sulfur cluster synthesis and disassembly; Iron-sulfur clusters as participants in reactions; Role of the sulfane carrying IscS protein in organic systems.

Extensively or completely activated preparations of beef heart succinate dehydrogenase have been investigated by electron paramagnetic resonance (EPR) techniques at 6 to 97 K. Reductive titrations with dithionite and rapid kinetic studies were performed with various types of soluble and membrane-bound preparations of the enzyme. The following components were detected and their behavior analyzed: a free radical, presumably arising from the covalently bound flavin on reduction, two iron-sulfur centers of the ferredoxin type, the signals of which appear on reduction, and a high-potential iron-sulfur component, detectable in the oxidized state. The high-potential component was only detected in complex II and inner-membrane preparations. This component and one of the ferredoxin­type centers were present in amounts close to stoichiometric with the flavin and were reduced by substrate. The other ferredoxin­type center was present in amounts between 0.1 and 0.5 times that of the flavin and was reduced only by dithionite. Of the components reduced by succinate, however, only a fraction (up to 50% of the high-potential iron-sulfur center and 40-60% of the ferredoxin­type iron-sulfur center) was reduced within the turnover time of the enzymes, in complex II not more than about 10% of the flavin appeared in the semiquinone form at any time. Soluble, purified preparations behaved similarly except that the high-potential component was nearly or completely absent and extensive accumulation of the free radical occurred (up to 70 to 80% of the flavin) in titration and kinetic experiments. No significant difference was observed between the rates of semiquinone formation and the reduction of the ferredoxin­type or high-potential centers by the substrate. Also no qualitative differences in the properties studied in this work became apparent between preparations containing 4 or 8 iron atoms, respectively. [ABSTRACT FROM AUTHOR]

The sulfur-reducing bacterium Spirillum 5175 was investigated with regard to membrane constituents that might be part of the sulfur oxidoreductase which converts elemental sulfur to hydrogen sulfide. Regardless of the electron acceptor used for cultivation of the bacteria, i.e. elemental sulfur, fumarate, or nitrate (Sp. 5175S,F,N). the qualitative pattern of cytochromes and Fe-S proteins did not change significantly, as documented by ultraviolet/ visible and electron paramagnetic resonance spectroscopy of oxidized (as isolated) and reduced (dithionite) samples. With elemental sulfur the prominent cytochrome exhibited absorption maxima at 553, 522.5 and 426 nm in the reduced state. In fumarate-grown cells two prominent cytochromes were found with maxima at 561, 551, 530, 521 and 430 nm. Two b-type cytochromes with Em at –198 mV and —20 mV vs the standard hydrogen electrode were identified in the membrane fraction of Sp. 5175F. A yellow pigment was extracted and identified as a flexirubin-type pigment. Although present in large quantities, it seemed not to be involved in the reduction of elemental sulfur. Menaquinone, MK 6 (Mr 580) was the prominent quinone identified in Sp. 5175. Characterization of a second quinone was not attempted because of its much lower concentration. The membrane constituents of Sp. 5175 were solubilized by a variety of detergents and detergent mixtures. A colorimetric procedure with photochemically reduced phenosafranin as the electron donor and cysteamine trisulfide (RS-S-SR, R = —CH2CH2NH2) as the electron acceptor was used to detect sulfur oxidoreductase activity. Three membrane proteins of Sp. 5175 were purified: (1) an [NiFe] hydrogenase, homogeneous by SDS/ polyacrylamide gel electrophoresis, with electron paramagnetic resonance signals as isolated at gx,y,z = 2.01, 2.16, 2.33 (100 K), and a strong signal at g = 2.02 below 20 K; (2) a cytochrome b, Fe-S-dependent fumarate reductase, and (3) a protein apparently linked to the sulfur oxidoreductase activity. In contrast to fumarate reductase, no type cytochrome was present in the fractions exhibiting sulfur oxidoreductase activity. The presence of Fe-S centers was demonstrated by electron paramagnetic resonance spectroscopy at 10 K. It is not clear whether the c-type cytochrome in the same fractions is part of the sulfur-reducing apparatus of Sp. 5175. [ABSTRACT FROM AUTHOR]

Examines the catalytic reaction between the enzyme the lysine 2,3-aminomutase and the interconversion of L-...-lysine ans L-B-lysine. What the enzyme contains; Proceedings of the reaction; Characterization of enzyme.