Exchange of iodine-131-labeled chylomicron protein in vitro

¹ Section on Metabolism, National Heart Institute, National Institutes of Health, Bethesda, Maryland

Chylomicrons isolated from rat chyle were iodinated with iodine¹³¹ and the protein specific activity determined before and after incubation with normal rat serum. A marked decrease in chylomicron protein specific activity occurred during incubation because of adsorption of nonradioactive soluble serum protein as well as exchange of part of the labeled chylomicron protein with lipoprotein protein. Ultracentrifugal fractionation of serum after such incubation revealed significant radioactivity in all of the lipoprotein fractions, but with low specific activity reflecting dilution by larger protein pools. Serum proteins with density greater than 1.21 contained much less radioactivity.