Quantitative analysis of pulse-chase experiments using transient expression in COS-7 cells. Radiolabeled media and cell lysates were immunoprecipitated and electrophoresed on SDS-PAGE. Radioactivity of PLG protein bands on dried gels was measured using an image analyzer. The amount of radioactive PLG protein at the beginning of the experiment was assigned a value of 100%. The graphs represent the radioactivity recovered from cell lysates (A) and medium (B) at each time point. The values represent the mean ± SEM (standard error of the mean) of 3 or 4 independent experiments. The P value is given as * (significant, P < .05) and ** (highly significant, P < .01).