Platelet-derived angiostatin. (A) Coomassie brilliant blue–stained SDS-PAGE of fractions 16 and pooled fractions 17 and 18. Fractions were obtained by lysine-Sepharose affinity chromatography for angiostatin of pooled platelet releasates. (B) Linear regression analysis (plotted points and solid line; confidence interval, dotted lines) of 50 kDa angiostatin standard used to determine concentrations of affinity-purified platelet-derived angiostatin fractions.