Other Chemical Labeling Methods

Other methods of chemical labeling of reactive groups in proteins have been described. Lysine residues [-NH-CH(C4Hg-NH2)-CO-] are much more plentiful in proteins than cysteines (typically 3-8 % of all residues) 

An unusual approach to chemical tagging for purposes of identification and quantitation of proteins has been described (Ornatsky 2006) in proof-of-principle experiments. Very briefly, this approach uses chemical tags that contain one of a series of metal atoms (gold, europium, samarium or terbium) that are then detected and quantitated using inductively-coupled-plasma (ICP)-MS, a standard analytical technique for elemental metal analysis (Nelms 2005) that can provide very high sensitivity and precision. At present this approach is very much in its initial stages of development, but the sensitivity is such that single cell proteomics may not be out of reach. 

---

Then the coefficients in the balanced chemical equation can be used as factors in the factor-label method to convert from moles of one chemical to moles of any other in the equation ... 

Studies using radioactivity-labeled acrylonitrile indicate that acrylonitrile or its metabolites form covalent adducts with cellular macromolecules in most tissues. Studies to develop chemical or immunological methods for measuring these adducts would be especially valuable in detecting and perhaps even quantifying human exposure to acrylonitrile. Adverse health effects demonstrated following exposure to acrylonitrile, particularly acute exposures, were characteristic of cyanide toxicity. Because these effects are also indicative of exposure to many other toxicants, additional methods are needed for more specific biomarkers of effects of acrylonitrile exposure. 

Methods used to demonstrate the existence of membrane phospholipid asymmetry, such as chemical labelling and susceptibility to hydrolysis or modification by phospholipases and other enzymes, are rmsuitable for dynamic studies because the rates of chemical and biochemical reactions are of a different order compared to the transmembrane translocahon of the phospholipids. Indirect methods have therefore been developed to measure the translocation rate which are consequent on the loss of membrane phospholipid asymmetry. Thus time scales appropriate to rates of lipid scrambling under resting conditions or when the forces preserving the asymmetric phospholipid distribution are disturbed can be monitored. Generally the methods rely on detecting the appearance of phosphatidylserine on the surface of cells. Methods of demonstrating Upid translocation in mammalian cells has been the subject of a recent review (Bevers etal., 1999). 

Another consideration when choosing a detector is whether it is important to preserve the separated analytes, either for use or for further analysis. Some methods, such as evaporative laser scattering detection and mass spectrometry, destroy the sample during the measurement. Other methods, such as fluorescence or radiochemical detection, may require chemical labeling of the analytes ... 

The IEM double-labeling method described was performed with cells fixed in 2% paraformaldehyde and 0 04% glutaraldehyde, and embedded in Lowicryl K4M, LR White, or LR Gold. Other fixation and embedding procedures should work equally well, provided that the specimen resists the chemicals used m the silver enhancement. 

Other includes Hazchem (spillages of hazardous chemicals, disposal methods, preventive procedures, MSDS request, etc.), labelling and scheduling queries, plant identification, etc. 

---