ANALYSIS OF 3-MERCAPTOPYRUVATE SULFURTRANSFERASE (3-MST).  A RESEARCH PROJECT MATERIAL ON BIOCHEMISTRY

ANALYSIS OF 3-MERCAPTOPYRUVATE SULFURTRANSFERASE (3-MST).  A RESEARCH PROJECT MATERIAL ON BIOCHEMISTRY

CHAPTERONE

1.0.         INTRODUCTION AND LITERATURE REVIEW

1.1.         INTRODUCTION

One of the major metabolic enzymes that have gained so much interest of scientists is 3-Mercaptopyruvate sulfurtransferase (3-MST). This enzyme occurs widely in nature (Bordo, 2002 and Jarabak, 1981).

It has been reported in several organisms ranging from humans to rats, fishes and insects. It is a mitochondrial enzyme which has been concerned in the detoxification of cyanide, a potent toxin of the mitochondrial respiratory chain (Nelson et al., 2000). Among the several metabolic enzymes that carry out xenobiotic detoxification, 3-mercaptopyruvate sulfurtransferase is of utmost importance.

3-mercaptopyruvate sulfurtransferase functions in the detoxifications of cyanide; mediation of sulfur ion transfer to cyanide or to other thiol compounds.(Vandenet al., 1967).It is also required for the biosynthesis of thiosulfate. In combination with cysteine aminotransferase, it contributes to the catabolism of cysteine and it is important in generating hydrogen sulphide in the brain, retina and vascular endothelial cells (Shibuyaet al., 2009). It also acquired different functions such as a redox regulation (maintenance of cellular redox homeostasis) and defense against oxidative stress, in the atmosphere under oxidizing conditionsNagaharaet al (2005).

Hydrogen sulphide (H₂S) is an important synaptic modulator, signalling molecule, smooth muscle contractor and neuroprotectant (Hosokiet al., 1997). Its production by the 3-mercaptopyruvate sulfurtransferase and cysteine aminotransferase pathways is regulated by calcium ions (Hosokiet al., 1997).

Organisms that are exposed to cyanide poisoning usually have this enzyme in them. This could be in food as in the cyanogenicglucosides being consumed. It has been studied from variety of sources, which include bacteria, yeasts, plants, and animals (Marcus Wischik, 1998).

Cyanide could be released into the bark of trees as a defence mechanism. There are array of defensive compounds that make their parts (leaves, flowers, stems, roots and fruits) distasteful or poisonous to predators. In response, however, the animals that feed on them have evolved over successive generations a range of measures to overcome these compounds and can eat the plant safely. The tree trunk offers a clear example of the variety of defences available to plants (Marcus Wischik, 1998).

Oryctes rhinoceros larva is one of the organisms that are also exposed to cyanide toxicity because of the environment they are found.

1.2.         3-MERCAPTOPYRUVATE SULFURTRANSFERASE

3-Mercaptopyruvate sulfurtransferase (EC. 2.8.1.2), is a member of the group, Sulfurtransferases (EC 2.8.1.1 – 5), which are widely distributed enzymes of prokaryotes and eukaryotes (Bordoand Bork, 2002).

3-Mercaptopyruvate Sulfurtransferase is an enzyme that is part of the cysteine catabolic pathway. The enzyme catalyzes the conversion 3-mercaptopyruvate to pyruvate and H₂S (Shibuya et al., 2009). The deficiency of this enzyme will result in elevated urine concentrations of 3-mercaptopyruvate as well as of 3-mercaptolactate, both in the form of disulfides with cysteine(Crawhallet al., 1969). It catalyzes the chemical reaction:

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ANALYSIS OF 3-MERCAPTOPYRUVATE SULFURTRANSFERASE (3-MST).  A RESEARCH PROJECT MATERIAL ON BIOCHEMISTRY