Rhodanese from Cercopithecus aethiops (vervet monkey) liver—II. Aspects of enzyme kinetics and mechanism of action

Among sulfur compounds, thiosulfate and polythionates are present at least transiently in many environments. These compounds have a similar chemical structure and their metabolism appears closely related. They are commonly used as energy sources for photoautotrophic or chemolithotrophic microorganisms, but their assimilation has been seldom studied and their importance in bacterial physiology is not well understood. Almost all bacterial strains are able to cleave these compounds since they possess thiosulfate sulfur transferase, thiosulfate reductace or S‐sulfocysteine synthase activities. However, the role of these enzymes in the assimilation of thiosulfate or polythionates has not always been clearly established. Elemental sulfur is, on the contrary, very common in the environmental. It is an energy source for sulfur‐reducing eubacteria and archaebacteria and many sulfur‐oxidizing archaebacteria. A phenomenon still not well understood is the ‘excessive assimilatory sulfur metabolism’ as observed in methanogens which perform a sulfur reduction which exceeds their anabolic needs without any apparent benefit. In heterotrophs, assimilation of elemental sulfur is seldom described and it is uncertain whether this process actually has a physiological significance. Thus, reduction of thiosulfate and elemental sulfur is a common by incompletely understood feature among bacteria. These activities could give bacteria a selective advantage, but futher investigations are needed to clarify this possibility. Presence of thiosulfate, polythionates and sulfur reductase activities does not imply obligatorily that these activities play a role in thiosulfate, polythionates or sulfur assimilation as these compounds could be merely intermediates in bacterial metabolism. The possibility also exists that the assimilation of these sulfur compounds is just a side effect of an enzymatic activity with a completely different function.

show abstract

“…Enz-S-S-+ A-~ Enz-S-+ A-S-It has been shown that these reactions correspond to a double displacement mechanism [30,33].…”

Section: S~o~-+ E~-s--+ En~-ss-+ So~-mentioning

confidence: 99%

Thiosulfate, polythionates and elemental sulfur assimilation and reduction in the bacterial world

Faou

Rajagopal

Daniels

et al. 1990

FEMS Microbiology Letters

View full text Add to dashboard Cite

show abstract

“…It is believed that rhodanese, an enzyme found primarily in the mitochondria, is chiefly responsible for the conversion of cyanide to thiocyanate in the body. This sulfur transfer by rhodanese is a classic example of a ping pong mechanism (5) and is illustrated in Scheme 1. The first step in the catalytic cycle, as labeled in Scheme 1, is the binding of a sulfur donor to rhodanese.…”

Section: Introductionmentioning

confidence: 99%

Disulfides as Cyanide Antidotes: Evidence for a New In Vivo Oxidative Pathway for Cyanide Detoxification

Zottola

Beigel

Soni

et al. 2009

Chem. Res. Toxicol.

View full text Add to dashboard Cite

It is known that cyanide is converted to thiocyanate in the presence of the enzyme rhodanese. The enzyme is activated by sulfur transfer from an appropriate sulfur donor. The activated enzyme then binds cyanide and transfers the sulfur atom to cyanide to form thiocyanate. This project began as an exploration of the ability of disulfides to act as sulfur donors in the rhodanese-mediated detoxification of cyanide. To our surprise, and contrary to expectations based on efficacy studies in vivo, our in vitro results showed that disulfides are rather poor sulfur donors. The transfer of a sulfur atom from a disulfide to the enzyme must occur via cleavage of a carbon-sulfur bond either of the original disulfide or in a mixed disulfide arising from the reaction of rhodanese with the original disulfide. Extending the reaction time and addition of chloride anion (a nucleophile) did not significantly change the results of the experiment. Using ultrasound as a means of accelerating bond cleavage also had a minimal effect. Those results ruled out cleavage of the carbon-sulfur bond in the original disulfide but did not preclude formation of a mixed disulfide. S-Methyl methylthiosulfonate (MTSO) was used to determine whether a mixed disulfide, if formed, would result in transfer of a sulfur atom to rhodanese. While no thiocyanate was formed in the reaction between cyanide and rhodanese exposed to MTSO, NMR analysis revealed that MTSO reacted directly with cyanide anion to form methyl thiocyanate. This result reveals the body's possible use of oxidized disulfides as a first line of defense against cyanide intoxication. The oxidation of disulfides to the corresponding thiosulfinate or thiosulfonate will result in facilitating their reaction with other nucleophiles. The reaction of an oxidized disulfide with a sulfur nucleophile from glutathione could be a plausible origin for the cyanide metabolite 2-aminothiazoline-4-carboxylic acid.

show abstract

Rhodanese from Cercopithecus aethiops (vervet monkey) liver—I. Purification and some physical characteristics

Rensburg¹,

Schabort²

1984

International Journal of Biochemistry

View full text Add to dashboard Cite

Rhodanese from Cercopithecus aethiops (vervet monkey) liver—II. Aspects of enzyme kinetics and mechanism of action

Cited by 7 publications

References 5 publications

Thiosulfate, polythionates and elemental sulfur assimilation and reduction in the bacterial world

Thiosulfate, polythionates and elemental sulfur assimilation and reduction in the bacterial world

Disulfides as Cyanide Antidotes: Evidence for a New In Vivo Oxidative Pathway for Cyanide Detoxification

Rhodanese from Cercopithecus aethiops (vervet monkey) liver—I. Purification and some physical characteristics

Contact Info

Product

Resources

About