BIO101 (Principles of Biology)
6 July 2012
The biochemical pathways of heavy metal poisoning are routes by which the metals pass in the body as they impair and destroy normal cellular and organ activity. The most common types of heavy metal poisoning are caused by lead, arsenic, cadmium and mercury. They are also the most extensively studied at the moment. Lead poisoning occurs mainly by the inhibitory effect that the metal imposes on enzymes and subsequent distortion of essential biochemical pathways. The metal disrupts calcium metabolism and subsequently causes neurotoxicity. It also inhibits the reduction of glutathionine in a biochemical process meant to produce antioxidants. Lead also intrudes and redirects the heme synthesis pathway leading to build up of aminolevulinic acid (ALA) in the cell. This results in the production of Reductive Oxygen Species (ROS) that mediate cell injury. Arsenic poisoning leads to the impairment of intracellular and intercellular communication pathways. Its effect on signal transduction leads to build up of free radicals that mediate cell death or injury. Mercury poisoning results from methylmercury. It has inhibitory effects that resemble those of lead and uniquely induces the release of free radicals in cells. Cadmium mainly poisons the cell by displacing essential nutrients such as calcium, zinc, iron and copper from biomolecules. The displaced metals are precipitated in body fluids and tissues and may be excreted or accumulate in the body. The biochemical pathways by which metal poisoning occurs mainly involve inhibition of biosynthetic, regulatory and other forms of enzyme activities, altered signal transduction pathways, induction of the production of free radicals and displacement biochemical reactions.
Biochemical Pathways of Heavy Metals Poisoning
Heavy metal poisoning is one of the most devastating health hazards that stems from environmental pollution. Industrial, agricultural and medical procedures contribute to the increase in exposure of people to heavy metals. Their poisoning impairs body systems like the renal system and the central nervous system which often fail as a result inhibition of the activity of essential enzymes, disruption of cell membrane's integrity or interference of protein synthesis by the metals. The metals and their derivatives also cause toxicology by disrupting of transcription and translation of genetic information as well as the inhibition of neurological processes through blocking of neurotransmitters. Protein
Heavy metals interfere with biochemical pathways by intruding the chemical structure of protein substrates, enzymes and some other influential reactants. Protein
SH S + M2+ M + 2H+ (M is the metal) E-M
SH S The above intramolecular reaction interferes with the reactivity of the thiol group and also occurs in enzymes as well as within individual amino acids. They also bind to active sites of enzymes and inhibit their biochemical activity by forming a stable enzyme-metal complex (E-M). + S + Product + S + S...