Isethionic acid

Abstract: Taurine is one of those enigmatic substances about which so much, and so little, is known. It is a simple substance, with a molecular weight of 125 and a molecular formula of C2H7O3NS. Taurine occurs in high concentration in many mammalian tissues, comprising in excess of 60% of the total free amino acid pool in the rat heart. Furthermore, it is one of the most abundant amino acids in the brain. Taurine, which was first isolated from bull’s urine in 1827 (Tiedemann and Gmelin, 1827), is a substance of high chemical stability and low metabolic reactivity. In mammals, only one potential pathway for the degradation of taurine has been proposed, that being the conversion to isethionic acid, but the evidence for this pathway is tenuous (Huxtable, 1978). Analysis of taurine can be readily achieved by a number of simple colorimet-ric tests in the laboratory, or it can be detected by an amino acid analyzer, on which it is one of the first substances eluted.

Abstract: The effects of taurine on ATP-dependent calcium ion uptake and protein phosphorylation of rat retinal membrane preparations were investigated. Taurine (20 mM) stimulates ATP-dependent calcium ion uptake by twofold in crude retinal homogenates. In contrast, it inhibits the phosphorylation of specific membrane proteins as shown by acrylamide gel electrophoresis and autoradiography. The close structural analogue of taurine, 2-aminoethylhydrogen sulfate, demonstrates similar effects in both systems, i.e., stimulation of ATP-dependent calcium ion uptake and inhibition of protein phosphorylation, whereas isethionic acid and guanidinoethanesulfonate have no effect on either system. A P1 subcellular fraction of the retinal membrane preparation that contains photoreceptor cell synaptosomes has a higher specific activity for the uptake of calcium ions. Phosphorylation of specific proteins in the P1 fraction is also inhibited by the addition of 20 mM taurine. Taurine has no effect on retinal ATPase activities or on phosphatase activity, thus suggesting that it directly affects a kinase system.

Abstract: This article presents a short review of recent research that established the ability of sulfate‐reducing bacteria to utilize sulfonic acids as terminal electron acceptors (TEA) for anaerobic respiratory growth. Newer studies of the bacterium most intensively investigated, Desulfovibrio desulfuricans, strain ICI, are also reported. When either of two sulfonic acids examined—isethionate (2‐hydroxyethanesulfonate) or cysteate (alanine‐3‐sulfonate)—served as sole TEA, key changes in the cells’ enzymo‐logical profile occurred: decreased production of two enzymes involved in sulfate reduction, namely, ATP sulfurylase and APS reductase. Similar reduction in content of these enzymes was seen when either sulfite or fumarate served as TEA. Protein profiles (polyacrylamide gel electrophoresis) of extracts of cells grown with different TEA revealed the presence of a 97‐kD polypeptide apparently unique to isethionate‐grown cells; a different polypeptide was noted in extracts of cysteate‐grown cells. The absence of such stained bands in extracts of sulfate‐grown cells suggests that these polypeptides are involved in utilization of sulfonic acids as TEA. H2 threshold values of cells growth with isethionate as TEA were significantly lower than for cells growing with sulfate or sulfite, suggesting that energy may be conserved in the cleavage of isethionate's C‐S linkage. A survey of the distribution of sulfonic acids in diverse habitats combined with the ability of other anaerobic bacteria to respire these compounds leads to the suggestion sulfonate reduction is likely to be significant in the sulfur cycle.