Labeling of high density lipoproteins with [3H] acetic anhydride

Rat serum HDL was labeled by reaction with [3H] acetic anhydride at pH 7.2 for 30 min at room temperature by a modification of the method of Montelaro and Rueckert (1975. J. Biol. Chem. 250: 1413). Protein specific activities of 60 dpm/ng were achieved. Seven percent of the label was in lipid, of which 92 percent was recovered in phospholipid. The labeled HDL migrated as a single band as seen by electrophoretic or column chromatographic analysis. When the labeled HDL was injected into rats without re-isolation, the biological half-life was not significantly different from HDL labeled in vitro with 125I or in vivo with amino acids. All of the apoproteins were labeled; their specific activities were closer to one another than those obtained with 125I. For some applications, acetylation may provide a useful alternative to the 125I labeling procedure.