Acid labile sulfide

Warenycia MW, Goodwin LR, Francom DM, et al. 1990. Dithiothreitol liberates non-acid labile sulfide from brain tissue of hydrogen sulfide-poisoned animals. Arch Toxicol 64 650-655. 

The bridging sulfur atoms in iron-sulfur proteins are often referred to as acid-labile sulfides, because treatment of such proteins with acids generates H2S. 

DEGREE OF DISSOCIATION HENDERSON-HASSELBALCH EQUATION ACID-BASE EQUILIBRIUM CONSTANTS BR0NSTED THEORY LEWIS ACID ACIDITY FUNCTION LEVELING EFFECT ACIDITY FUNCTION ACID-LABILE SULFIDES ACID PHOSPHATASE ACONITASE... 

Two unusual rubredoxins are known at present, from D. gigas and Pseudomonas oleovorans. Both have two iron centres but differ from each other. The rubredoxin from D. gigas (desul-foredoxin) has a molecular weight of 7900, with no acid labile sulfide and eight cysteine residues.744 The electronic spectrum is different from that of the two-iron rubredoxin from P. oleovorans in that it is not simply the addition of two spectra of one-iron rubredoxins. These additional features have led to the suggestion that the two iron centres interact. 

All iron-sulfur proteins, whether of the plant-type or the bacterial-type have three characteristics in common all contain the acid-labile sulfide in equimolar ratio to iron all show reduction potentials in the range from —240 to —420 mV (E0,pli = 7.0) and when these proteins are chemically-reduced (typically with dithionite), they display an uncommon EPR signal, known as the g = 1.94 signal. The oxidized forms of the proteins are not paramagnetic (159). 

Adenylyl sulfate (APS) reductase is a flavoprotein, which contains iron and possibly acid-labile sulfide. It catalyzes the reduction of APS in the... 

Whereas Peck and his co-workers have not reported the presence of acid-labile sulfide in the APS reductase of D. vulgaris, Lyric and Suzuki (376) have shown that the enzyme from Thiobacillus thioparus contains 4-5 moles of labile sulfide per mole. The T. thioparus enzyme appears to have a molecular weight of 170,000, and contains, in addition to labile sulfide, 1 mole of FAD and 8-10 g-atoms of iron per mole. That the en-... 

VIII Recent data of Bramlett and Peck (434) indicate that, as predicted in the above review, the adenylyl sulfate reductase of Desvlfovibrio vulgaris does contain acid-labile sulfide. The enzyme with a molecular weight of 220,000 has been shown to contain 1 mole of FAD, 12 g-atoms of iron and 12 moles of labile sulfide per mole. In addition, SDS-gel electrophoresis has revealed the presence of subunits with molecular weights of 20,000 and 72,000. 

The best studied Cd-y-EC peptide complexes containing acid labile sulfide as an additional component were isolated from yeasts S. pombe and Candida glabrata where y-EC peptides were shown to coat the CdS particles. Ratios of S Cd in these heterogenous complexes vary from 0.1 to 0.6. This diversity is paralleled by a nondiscrete variation in apparent molecular mass between about 3500-6400 Da, determined by gel exclusion chromatography. These complexes exhibit a red-shifted absorption profile with a new band in the near-UV region (between 270-320nm) when compared to the... 

The succinate dehydrogenase of S. acidocaldarius (DSM 639) is located in the cytoplasmic and membrane fractions when cells are disrupted either by sonication or decompressive disruption. About 10-30% of the activity is associated with the membrane fraction [30]. The purified membrane-bound succinate dehydrogenase activity (M, 141 000) consists of four subunits (Mr 66000, 31 000, 28 000, and 12,800). The enzyme contains a covalently-bound flavin as well as iron and acid-labile sulfide but no cytochrome [111]. The dehydrogenase reduces the following acceptors (listed in order of decreasing... 

Meanwhile, H0j andMpller radioactively labeled the thylakoid membrane hy growing barley in the presence of and S04 . The labeled PS-1 particles were found to contain 10 Fe-atoms and 14 acid-labile sulfides per P700. SDS-PAGE analysis showed that there was a high cysteine content in the 8-kDa polypeptide and that 4 Fe atoms were present in the 110-kDa heterodimer of PsaA/PsaB. 

The presence of four non-heme iron atoms and four acid-labile sulfides in the PS-I core complex could be accounted for by either one [4Fe 4S ] cluster or two [2Fe 2S] clusters. However, two [ 2Fe 2S] clusters can not be accommodated by the limited number of cysteine residues available on the PsaA and PsaB subunits, since in all known cases there are fewer than 8 cysteines on the PsaA and PsaB subunits combined [see the amino-acid sequence in Fig. 11 below]. In a sense, the structure and number of iron-sulfur clusters coordinated jointly to the PsaA and PsaB subunits have a critical implication for the structure of the PS-I reaction center itself. 

The reduction of the sulfoxides generates acid-labile sulfides. 

Aconitase was first suggested to have an iron-sulfur cluster by virtue of the presence of acid-labile sulfide, as well as a g = 2.01 EPR signal, in the purified protein. The iron-sulfur cluster giving rise to this g = 2.01 signal was later shown to be a [3Fe-4S]" " cluster, and was characteristic of inactive enzyme. " " Activation by addition of iron and reductant, or by addition of reductant alone, provided the enzymatically active aconitase, although in the latter case only approximately 75% of full activity was obtained. As the active form of aconitase was subsequently shown to be the [4Fe-4S] form, " addition of iron and reductant provided the iron needed to occupy the fourth metal site in the cluster, while addition of reductant alone resulted in rearrangement of the clusters, labilizing iron to allow reassembly of [4Fe-4S] clusters in 3/4 of the cluster sites. 

A major step in resolving this incompatibility was the unexpected discovery that PSN2OR and PapN20R contained acid-labile sulfide present at 1.7 0.4 atoms per dimer, not found in mutated protein lacking Cuz centers.Resonance Raman data for PSN2OR indicated that Cuz contained a Cu—S bond. A prominent band at 382 cm was sensitive to the substitution of by (isotope shift —5.8cm ), but not by isotopic substitution of Cu by Cu or... 

The PSI-C polypeptide has a molecular mass of 9 kDa and binds the iron-sulfur clusters A and B (4). The first proposal of the PSI-C polypeptide as being an iron-sulfur protein was based on its high cysteine content (37). The protein was isolated from PS I particles of barley and shown to carry zero-valence sulfur which is indicative for a denatured iron-sulfur center (4). The amount of zero-valence sulfur bound to the polypeptide corresponded to 8 acid-labile sulfides per molecule (4). The N-terminal amino acid sequence of the isolated protein permitted the identification of its corresponding chloroplast gene which... 

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