Sulfur, biological role

T. Ubuka, Assay methods and biological roles of labile sulfur in animal tissues. B. Analyt Technol. Biomed. Life Sci. 781, 227-249 (2002). 

Rubredoxins. Rubredoxins are the simplest form of iron-sulfur proteins in which iron is bound to the sulfur atom of cysteine as shown in Fig. lA. One of the first rubredoxins isolated was from an anaerobic bacterium, Clostridium pasteurianum, by Lovenberg and Sobel (9). The protein is composed of 54 amino acids and has a molecular weight of 6,000. The oxidized form has absorbance maxima at 380 and 490 nm. The biological role of the rubredoxin isolated from C. pasteurianum is stiU unknown. 

The current status of nitrogenase metal-cluster modeling by synthetic inorganic clusters and complexes is reported here. Modeling is to be understood not only in terms of stmcture and associated spectroscopic properties, but also in terms of function, that is, how well the models reproduce, or help to understand, the biological role of the metal-sulfur assembhes in nitrogenase, that is, electron transfer and the reduction of substrates. 

The elements of groups 13—16 fall into three categories (Fig. 1.3), the metalloids, the other metals, and the nonmetals. The important biological role of some of the nonmetals, oxygen, nitrogen, phosphorus, sulfur, and selenium together with the halogens, chlorine and iodine, will be discussed in Chapter 18. 

Phosphoric and sulfuric acid derivatives possess crucial properties that allow them to uniquely fill their many roles in biochemistry. Phosphoric acid may be esterified to form a monoester, diester, or triester (Figure 1). Sulfuric acid may be esterified at one or two positions, to form a monoester or a diester. Sulfate diesters are highly reactive, and have not been found in nature nor do phosphate triesters occur naturally. The hydrolysis of both phosphate and sulfate esters are thermodynamically favorable, but nucleophiles are repelled by the negative charge of the ionized forms. The resulting kinetic stability of phosphate monoesters and diesters, and of sulfate monoesters, is a major factor in their suitability for biological roles. For example, the half-life for hydrolysis of alkyl phosphate dianions by water is approximately 1.1 X 10 years k=2 x 10 s ) at 25°C. Such species... 

Antimony is a non essential element in the human body and it has no biological role. Its total amount existing in the body normally is about 2 mg, and 100 mg is the lethal limit. Antimony is very toxic, but it has also been prescribed as a treatment for different kinds of diseases for hundreds of years. For example antimony has been used to treat several parasitic diseases such as Schistosomiasis caused by several species of flatworm in both humans and animals. Antimony is thought to attach itself easily to sulfur atoms of certain enzymes which are used by both the parasites and human body, and in small doses can kill the parasite without causing any damage to the patient. 

In conclusion, these results indicate that Sulfolobus solfataricus ceU-free system contains a significant ADP-ribosyl transferase activity. It seems of relevant interest that this archaebacterium is the most primitive organism in which ADP-ribosylation has been demonstrated. Furthermore the enzymatic activity appears to be thermophilic, a unique property never observed for the same kind of enzyme isolated from other sources (17). Further studies are in progress on the purification and characterization of the enzyme to investigate its biological role. As mentioned above, several biochemical properties demonstrated that sulfur-dependent archaebacteria are closer related to eukaryotes than to eubacteria (3). These findings support the hypothesis that the ADP-ribosyl transferase activity which we found associated primarily with the nucleoprotein fraction of Sulfolobus solfataricus, could play a role in any cellular event in which the enzyme is known to be involved in eukaryotic cells (17). 

Thiamine Pyrophosphate is the coenzyme responsible for transferring active acetaldehyde and active glycolaldehyde. Simultaneously, it acts as co-decarboxylase, i.e. as the coenzyme for a lyase. The characteristic component is thiamine (vitamin Bi), one of the vitamins whose biologic role has been known longest the symptoms of thiamine deficiency (beriberi in man polyneuritis in animals) comprised one of the starting points in the study of vitamins. The name thiamine refers to its sulfur content. 

Isotope effects also play an important role in the distribution of sulfur isotopes. The common state of sulfur in the oceans is sulfate and the most prevalent sulfur isotopes are (95.0%) and (4.2%). Sulfur is involved in a wide range of biologically driven and abiotic processes that include at least three oxidation states, S(VI), S(0), and S(—II). Although sulfur isotope distributions are complex, it is possible to learn something of the processes that form sulfur compounds and the environment in which the compounds are formed by examining the isotopic ratios in sulfur compounds. 

The following sections summarize only the most prominent interactions between the elemental cycles and the links in the hydrologic cycle. Water also plays a role in many chemical and biological reactions that are beyond the scope of this discussion. The carbon, nitrogen, sulfur, and phosphorus cycles are discussed in detail in Chapters 11, 12, 13, and 14, respectively. 

Therefore, polysulfide ions play a major role in the global geological and biological sulfur cycles [1, 2]. In addition, they are reagents in important industrial processes, e.g., in desulfurization and paper production plants. It should be pointed out however that only sulfide, elemental sulfur and sulfate are thermodynamically stable under ambient conditions in the presence of water, their particular stabihty region depending on the redox potential and the pH value [3] ... 

Fe-4S] + + clusters are certainly the most ubiquitous iron-sulfur centers in biological systems. They play the role of low potential redox centers in ferredoxins, membrane-bound complexes of the respiratory... 

---