Methods for assessment of tissue sites of lipoprotein degradation

Publisher Summary This chapter describes various methods for assessments of tissues sites of lipoproteins degradation. At the present time the method of choice for most applications seems to be the tyramine-cellobiose technique. Tyramine, the radioiodine acceptor, is linked to cellobiose, a non hydrolyzable reducing disaccharide, by reductive amination. The resulting tyramine-cellobiose adduct (TC) is then attached to the protein using cyanuric chloride. Two biological requisites must be met for the trapped label approach to be applicable. First, the tracer must be metabolically indistinguishable from the tracer protein, at least through the step of irreversible removal from plasma. Second, the labeling ligand must be adequately trapped in the cells degrading the labeled protein. The TC ligand appears to leak from catabolizing cells at a rate of about 10%/day, somewhat more than the approximately 5%/day observed with the sucrose ligand. This method was developed to provide a higher specific activity label. The major limitation to labeling proteins to high specific activity by this method is the need to deal with chemically manipulatable quantities of reagents, which in turn necessitates the handling of relatively large amounts of radioactivity.