Cellular toxins

Membrane proteins carry out a wide range of critical functions in cells, and they include passive and active transporters, ion chamiels, many classes of receptors, cellular toxins, proteins involved in membrane trafficking, and the enzymes that facilitate electron transport and oxidative phosphorylation. For example, the voltage-gated ion channels that facilitate the passive diffusion of sodium and potassium across the axonal membrane are responsible for the formation of an action potential. Active transport proteins establish ion gradients and are necessary for the uptake of nutrients into cells. Soluble hormones bind to membrane receptors, which then regulate the internal biochemistry of the cell. 

Cyanide is described as a cellular toxin because it inhibits aerobic metabolism. It reversibly binds with ferric (Fe " ") iron-containing cytochrome oxidase and inhibits the last step of mitochondrial oxidative phosphorylation. This inhibition halts carbohydrate metabolism from citric acid cycle, and intracellular concentrations of adenosine triphosphate are rapidly depleted. When absorbed in high enough doses, respiratory arrest quickly ensues, which is probably caused by respiratory muscle failure. Cardiac arrest and death inevitably follow. 

About ten years ago scientists studying muscle relaxation discovered that our bodies produce nitric oxide for use as a neurotransmitter. (A neurofransmitter is a small molecule that serves to facilitate cell-to-cell communications.) Since then, it has been detected in at least a dozen cell types in various parts of the body. Cells in the brain, the liver, the pancreas, the gastrointestinal tract, and the blood vessels can synthesize nitric oxide. This molecule also functions as a cellular toxin to kill harmful bacteria. And that s not all In 1996 it was reported that NO binds to hemoglobin, the oxygen-carrying protein in the blood. No doubt it helps to regulate blood pressure. 

Vaughan and Nory. Cellular Toxins (Text), Philadelphia, 1902. 

Blum, P.C., Henry, M.S., Pierce, R.H., Payne, S.R., and Lyons, J.I. Intra-cellular and extra-cellular toxins in the red tide dinoflagellate, Gymnodinium breve, J. Phycol, 36, 7-7, 2000. 

Sodium azide (hydrazoic acid, sodium salt NaNj [CAS 26628-22-8]) Potent cellular toxin inhibits cytochrome oxidase. Eye irritation, bronchitis, headache, hypotension, and collapse have been reported in overexposed workers. See also p 122. 0.29 mg/m (C) (as sodium azide) 0.11 ppm (C) (as hydrazoic acid vapor) Vifhite, odorless, crystalline solid. 

The cardenolides within the monarch butterfly s tissues are tightly bound to the cuticle in the various organs. Presumably, this is a mechanism to avoid self-poisoning and to keep these cellular toxins away from neuronal tissues (Harbome, 1991). 

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