Enzymes Of Sulfur Metabolism Research Articles

The functional role of reduced inorganic sulfur compounds in the metabolism of the microaerophilic bacterium Spirillum winogradskii

Oxidation of reduced sulfur compounds by microaerophilic sulfur bacterium Spirillum winogradskii was found to occur only concomitantly with consumption of an organic substrate and was not linked to their utilization as electron donors in energy metabolism. No enzymes of dissimilatory sulfur metabolism were found in the cells of the sulfur bacterium oxidizing thiosulfate to tetrathionate; oxidation of thiosulfate and sulfide was caused by their reaction with reactive oxygen species (ROS), mostly H2O2 produced in the course of aerobic growth. Decreased lytic effect of ROS in the presence of thiosulfate resulted in a twofold increase in the cell yield under aerobic conditions and more efficient substrate utilization. The latter effect was caused by decreased expense of energy for the biosynthesis of oxygen-protecting polysaccharides. The stimulatory effect of thiosulfate on the growth processes was due to the activation of a number of TCA cycle enzymes producing the intermediates for constructive metabolism, especially of the NADP-dependent malic enzyme. As a result of thiosulfate-induced synthesis of SH-containing cell components, the integral antioxidative activity increased 1.5-fold.

Effect of Cultivation Conditions on the Growth and Activities of Sulfur Metabolism Enzymes and Carboxylases of Sulfobacillus thermosulfidooxidans subsp. asporogenes Strain 41

The moderately thermophilic acidophilic bacterium Sulfobacillus thermosulfidooxidans subsp. asporogenes strain 41 is capable of utilizing sulfides of gold-arsenic concentrate and elemental sulfur as a source of energy. The growth in the presence of S0 under auto- or mixotrophic conditions was less stable compared with the media containing iron monoxide. The enzymes involved in oxidation of sulfur inorganic compounds--thiosulfate-oxidizing enzyme, tetrathionate hydrolase, rhodonase, adenylyl sulfate reductase, sulfite oxidase, and sulfur oxygenase--were discovered in the cells of Sulfobacillus grown in the mineral medium containing 0.02% yeast extract and either sulfur or iron monoxide and thiosulfate. Cell-free extracts of the cultures grown in the medium with sulfur under auto- or mixotrophic conditions displayed activity of the key enzyme of the Calvin cycle--ribulose bisphosphate carboxylase--and several other enzymes involved in heterotrophic fixation of carbonic acid. Activities of carboxylases depended on the composition of cultivation media.

Sulfur-Metabolizing Enzymes in Thermoacidophilic Bacteria Sulfobacillus sibiricus

Sulfur oxygenase, sulfite oxidase, adenylyl sulfate reductase, rhodanase, sulfur : Fe(III) oxidoreductase, and sulfite : Fe(III) oxidoreductase were found in cells of aerobic thermoacidophilic bacteria Sulfobacillus sibiricus, strains N1 and SSO. Enzyme activity was revealed in the cells grown on medium with elemental sulfur or in the presence of various sulfide minerals and concentrates of sulfide ores. The activity of enzymes of sulfur metabolism depended little on the degree of aeration during bacterial growth.

Strategies for the allocation of resources under sulfur limitation in the green alga Dunaliella salina.

The effect of sulfur limitation on the partitioning of carbon, nitrogen, and sulfur was investigated in Dunaliella salina. D. salina was able to adapt to 6 microM sulfate; under these conditions, the cells showed reduced growth and photosynthetic rates. Whereas intracellular sulfate was depleted, phosphate, nitrate, and ammonium increased. Amino acids showed a general increase, and alanine became the most abundant amino acid. The activities of four key enzymes of carbon, sulfur, and nitrogen metabolism were differentially regulated: Adenosine 5' triphosphate sulfurylase activity increased 4-fold, nitrate reductase and phosphoenolpyruvate (PEP) carboxylase activities decreased 4- and 11-fold, respectively, whereas carbonic anhydrase activity remained unchanged. Sulfur limitation elicited specific increase or decrease of the abundance of several proteins, such us Rubisco, PEP carboxylase, and a light harvesting complex protein. The accumulation of potentially toxic ammonium indicates an insufficient availability of carbon skeletons. Sulfur deficiency thus induces an imbalance between carbon and nitrogen. The dramatic reduction in PEP carboxylase activity suggests that carbon was diverted away from anaplerosis and possibly channeled into C3 metabolism. These results indicate that it is the coordination of key steps and components of carbon, nitrogen, and sulfur metabolism that allows D. salina to adapt to prolonged sulfur limitation.

Lithoheterotrophic growth and electron transfer chain components of the filamentous gliding bacteriumLeucothrix mucorDSM 2157 during oxidation of sulfur compounds

Evidence is presented that the type strain of filamentous gliding bacterium Leucothrix mucor DSM 2157 is capable of lithoheterotrophic growth. Thiosulfate oxidation was accompanied by accumulation of sulfate and tetrathionate in the growth medium and intracellular accumulation of elemental sulfur, as occurs in filamentous sulfur bacteria of the genus Thiothrix. Thiosulfate oxidation by L. mucor was induced during growth with a limiting concentration of organic substrate (i.e. 50–170 mg l−1 tryptone) and resulted from the induction of dissimilatory enzymes of sulfur metabolism. Metabolically useful energy was derived by both substrate-linked and oxidative phosphorylation from thiosulfate and sulfite oxidation. During sulfite oxidation the electron transfer pathway was shown to begin at the ubiquinone-cytochrome b segment of the electron transport chain. L. mucor limited by organic substrate had lowered levels of membrane bound cytochromes c and respiratory activity but a higher input of a cyanide-insensitive respiratory component than during organic enriched growth. Cytochromes aa3 and d, which had not been shown previously in this bacterium, were detected in the cells under various growth conditions. Cytochrome aa3 is suggested to take part in the electron transfer pathway from thiosulfate to oxygen which was completely inhibited by 100 μM cyanide.

Lithoheterotrophic growth and electron transfer chain components of the filamentous gliding bacterium Leucothrix mucor DSM 2157 during oxidation of sulfur compounds

Evidence is presented that the type strain of filamentous gliding bacterium Leucothrix mucor DSM 2157 is capable of lithoheterotrophic growth. Thiosulfate oxidation was accompanied by accumulation of sulfate and tetrathionate in the growth medium and intracellular accumulation of elemental sulfur, as occurs in filamentous sulfur bacteria of the genus Thiothrix. Thiosulfate oxidation by L. mucor was induced during growth with a limiting concentration of organic substrate (i.e. 50–170 mg l −1 tryptone) and resulted from the induction of dissimilatory enzymes of sulfur metabolism. Metabolically useful energy was derived by both substrate-linked and oxidative phosphorylation from thiosulfate and sulfite oxidation. During sulfite oxidation the electron transfer pathway was shown to begin at the ubiquinone-cytochrome b segment of the electron transport chain. L. mucor limited by organic substrate had lowered levels of membrane bound cytochromes c and respiratory activity but a higher input of a cyanide-insensitive respiratory component than during organic enriched growth. Cytochromes aa 3 and d, which had not been shown previously in this bacterium, were detected in the cells under various growth conditions. Cytochrome aa 3 is suggested to take part in the electron transfer pathway from thiosulfate to oxygen which was completely inhibited by 100 μM cyanide.

Thermotolerance of adenylylsulfate reductase fromThiobacillus denitrificans

Adenylylsulfate (APS) and APS reductase are important in the energy-generating processes of sulfate-reducing bacteria and sulfur lithotrophs (phototrophs and nonphototrophs). APS reductase from an extremely thermophilic archaebacterial sulfate-reducer was recently shown to be thermophilic with optimal activity at 85°C (Speich and Truper (1988) J. Gen. Microbiol. 134, 1419–1425). APS reductase of Thiobacillus denitrificans, a mesophilic eubacterium, has biochemical and physical properties in common with the thermophilic enzyme and is also thermotolerant (up to 75°C). APS reductase and other enzymes of dissimilative inorganic sulfur metabolism may commonly be thermotolerant is mesophilic eubacteria; perhaps a vestige of their primordial significance.

Persulfide sulfur is a growth factor for cells defective in sulfur metabolism.

Several systems which generate persulfide sulfur promote in vitro proliferation of L1210 murine lymphoma cells. The systems include cysteine disulfides and pyridoxal, cystamine and diamine oxidase, beta-mercaptoalcohol disulfides and an alcohol dehydrogenase, and sulfide-treated proteins and a thiol. Persulfide sulfur is very unstable at pH near 7 and an essential feature of the growth-supporting systems is the ability to generate persulfide sulfur at a very low rate for long periods of time. Methyl disulfides (R--S--S--CH3) also support growth of L1210 cells and are more stable than persulfides (R--S--S--H). The requirement for these sulfur groups by L1210 cells may be related to the fact that these cells are defective in at least two enzymes of sulfur metabolism, cystathionase and 5'-methylthioadenosine phosphorylase. These findings provide the first evidence that persulfide sulfur may have a physiological role.

Developmental regulation of choline sulfatase and aryl sulfatase in Neurospora crassa

Regulation of the synthesis of several enzymes of sulfur metabolism in Neurospora is a function of both metabolic regulation and the genetic control exerted by the cys-3 and scon regulatory genes. Additional control mechanisms appear to regulate the synthesis of choline sulfatase and aryl sulfatase in different developmental stages of the life cycle. The metabolic regulation of enzyme synthesis in conidia differs from that which occurs in the mycelial stage. During conidial germination and mycelial outgrowth, the synthesis of these enzymes is not coordinate but begins at different times and occurs at different rates. A rapid and early synthesis of choline sulfatase was observed during conidial germination under derepressing conditions; furthermore, synthesis of the enzyme also occurred for a brief period in germinating conidia even in the presence of repressing levels of sulfate. The results of this study suggest that several enzymes of sulfur metabolism are independently controlled by a developmental system which is superimposed upon the cys-3 regulatory mechanism. It was also found that choline sulfatase undergoes rapid turnover while aryl sulfatase is a stable species.

Control of the synthesis, activity, and turnover of enzymes of sulfur metabolism in Neurospora crassa

The synthesis of aryl sulfatase, choline- O-sulfate permease, and two distinct sulfate permeases are repressed by methionine, but the activity of these enzymes is not subject to feedback inhibition. The permease species, but not aryl sulfatase, are also regulated by dynamic turnover, displaying a functional half-life of approximately 2 hr. The rate of turnover of these permeases is not influenced by the presence of the end product, methionine. Development of sulfate permease activity occurs only by de novo synthesis which requires both a lifting of methionine repression and a functional cys-3 product. The turnover system for sulfate permease is not present in dormant conidia but appears to be synthesized relatively rapidly during germination. Preexisting conidial sulfate permease is lost by turnover during germination and outgrowth into the mycelial phase, during which both permease species are synthesized anew, although the high affinity system contributes most of the total activity in growing mycelia.

Novel mutation causing derepression of several enzymes of sulfur metabolism in Neurospora crassa.

A group of enzymes of sulfur metabolism (arylsulfatase, cholinesulfatase, and a number of others) are normally repressed in Neurospora crassa by an abundant supply of a "favored" sulfur source such as methionine or inorganic sulfate. A mutant called scon(c) was isolated in which the formation of each of these enzymes is largely or completely nonrepressible. The structural genes for three of these enzymes have been mapped; scon(c) is not linked to any of them. It is also not linked to cys-3, another gene which is involved in control of the same group of enzymes. Two alleles of the structural gene for arylsulfatase [ars(+) and ars(UFC-220)] produce electrophoretically distinguishable forms of arylsulfatase. Heterokaryons with the constitution scon(c) ars(+) + scon(+)ars(UFC-220) were prepared. These heterokaryons produce both forms of arylsulfatase under conditions of sulfur limitation, but produce only the wild-type (ars(+)) form under conditions of sulfur abundance. When the alleles of ars and scon are in the opposite relationship, only the ars(UFC-220) form of arylsulfatase can be detected under conditions of sulfur abundance. Thus the effect of the scon(c) mutation seems to be limited to its own nucleus. The implications of these findings are discussed.

Positive control by the cys-3 locus in regulation of sulfur metabolism in Neurospora

Three enzymes of sulfur metabolism are simultaneously lost in the cys-3 mutant of Neurospora. Revertants of cys-3 have been selected and appear to arise from mutation within the original locus. The revertants can be grouped into at least three classes according to the amounts of the enzymic activities that are restored and by temperature sensitivity. The properties of the revertant strains indicate that the cys-3 mutant is not a large deletion, a super-repressor mutation, or an extreme polar mutant; nor does the cys-3 locus code for a polypeptide chain common to the three enzymes. We suggest that cys-3 is a regulatory gene which exerts positive control over enzyme synthesis.