Radioisotopic techniques in lipidology

Abstract

This chapter is concerned with specialized radioisotopic procedures as they apply to studies of lipid material, namely, labelled precursors, incorporation of radioisotopic labels into lipids, isolation and separation of the labelled material, autoradiography, and counting. The most specific and universal precursor for labelling of long-chain hydrocarbon groups (normal, branched or isoprenoid chains) in cells, tissues or whole organisms is acetate labeled, either with 14C or 3H. With higher plants or algae, 14CO2 is used for this purpose and water-soluble moieties of lipids are labeled. Introduction of radioisotopes into cellular lipids is primarily dependent on the rate of turnover or biosynthesis of the lipids at the cellular level. The total labelled cellular or tissue lipids, obtained are fractionated and individual components are isolated by silicic acid and/or Diethylaminoethyl (DEAE) cellulose column chromatography or by preparative thin- layer chromatography (TLC). The radioisotopes commonly used to label lipids are β-particle emitters. Three general procedures are available for counting lipids labelled with these radioisotopes, using: (1) an end-window Geiger-Muller (GM) tube; (2) a gas-flow counter; or (3) a scintillation counter. Only a brief treatment of counting procedures, dealing mostly with sample preparation, is given here. Detection of radioactive lipids on chromatograms is achieved by autoradiography using X-ray film. © 1972, North-Holland Publishing Company