Carbodiimides cystamine

The carbodiimide of choice used to couple cystamine to carboxylate- or phosphate-containing molecules is most often the water-soluble carbodiimide, EDC hydrochloride Chapter 3, Section 1.1). This reagent rapidly reacts with carboxylates or phosphates to form an active ester intermediate, which is highly reactive toward primary amines. The reaction is efficient from pH 4.7 to 7.5, and a variety of buffers may be used, providing they don t contain competing groups. 

Figure 1.71 Cystamine may be used to label protein carboxylate groups using the water-soluble carbodiimide EDC.

Figure 1.72 Cystamine may be used to label phosphate groups, such as at the 5 -end of oligonucleotides, via a carbodiimide reaction using EDC. The resultant phosphoramidate linkage is a common way to modify oligonucleotides at the 5 -end.

DNA or RNA also may be modified with cystamine at the 5 -phosphate group using a carbodiimide reaction. See Chapter 27, Section 2.2 for a complete discussion of the labeling protocol. 

The surface matrix of a carboxymethylated sensor chip CMS (Pharmacia Biosensor, Uppsala, Sweden) was activated by injection of 35 pL of 0.05 M N-hydroxy-succinimide (NHS)/0.2 M N-ethyl-N (dimethylaminopropyl)carbodiimide (EDC). The BIAcore IFC forms four parallel flow cells on the sensor chip. Three of them were derivatized with 40 mM cystamin-dihydrochloride/ethanolamine in the ratios... 

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