Mercapturic acid

Mercapturic acid (also known as N-acetyl-L-cysteine conjugate) is a type of metabolite found in the urine of mammals. It is a product of the metabolism of many substances, including certain drugs and environmental toxins. The formation of mercapturic acid is a key step in the detoxification process of these substances.

Structure and Properties

Mercapturic acid is a carboxylic acid with a sulfur atom attached to the carbon chain. The sulfur atom is part of a thiol group, which gives mercapturic acid its name (from the Latin mercaptus, meaning "captured sulfur"). The molecule also contains an amino acid group, specifically cysteine, which is attached to the carbon chain via an acetyl group.

Biosynthesis

The biosynthesis of mercapturic acid involves several steps. First, a substance undergoes biotransformation to form a glutathione conjugate. This conjugate is then processed by the enzymes gamma-glutamyltransferase, cysteinylglycinase, and N-acetyltransferase to form the final mercapturic acid product.

Role in Detoxification

Mercapturic acid plays a crucial role in the detoxification of many substances. The formation of a mercapturic acid conjugate effectively neutralizes the toxicity of the original substance and makes it more soluble in water, allowing it to be excreted in the urine. This process is particularly important in the detoxification of drugs and environmental toxins.

Clinical Significance

The presence and quantity of mercapturic acid in the urine can be used as a biomarker for exposure to certain toxins or drugs. For example, the mercapturic acid derivative of acrolein, a toxic compound found in cigarette smoke, can be measured in the urine of smokers and used as an indicator of exposure to cigarette smoke.