Radiolabeling of amyloid-beta peptides.

Nowadays, a wide variety of protocols for labeling proteins is available. However, radiolabeling remains one of the most powerful, sensitive and accurate methods to trace and quantitate proteins. Additionally, radiolabeling techniques are steadily gaining importance for diagnosis and treatment in nuclear medicine. There is a considerable number of radioisotopes, but only some are commonly used for basic biomedical research. Among them, the iodine radioisotopes (gamma-emitters) have several advantages for the labeling of proteins. This chapter focuses on radioiodination protocols for amyloidogenic peptides, using the Abeta peptides as a paradigm. The chloramine T, Iodo-Gen, and lactoperoxidase methods can be successfully applied to radioiodination of different amyloid peptides as long as free tyrosyl (or histidyl) groups are avail-able. However, these methods differ in their yield and the degree of oxidative damage conferred to labile peptides. When no tyrosines are available, the Bolton-Hunter methodology can be used. The labeling by the tyramine-cellobiose ligand trapping method is applicable to the study of cellular uptake and catabolism of amyloid peptides.