Figure 1.

Precursor product relationship of two radiolabeled spots from microsomes separated on thin-layer chromatography (TLC). A, The radioactivity in products separated by one-dimensional TLC (see below for details) after a continuous 1-h assay for DGTS synthesis. B, The changes in radioactivity in the upper and lower products after the onset of a chase period. C, The relative activity expressed in percent remaining in each spot. The pulse-chase procedures involved presenting microsomal fractions with 130 μm [¹⁴C-carboxyl]- SAM (specific activity = 11 mCi/mmol) for 30 min, followed by the addition of 1.3 mm nonradioactive SAM. Aliquots were taken at indicated intervals after the latter addition, the lipids extracted as described in “Materials and Methods,” and the chloroform-soluble fraction was chromatographed on silica gel G TLC plates using chloroform:methanol:7 n NH₄OH (65:35:4, v/v). Spots were visualized with I₂ vapors and those of interest were scraped from the plates into scintillation vials for the determination of radioactivity.