Drm/gremlin purification from the CM of FGF2-T-MAE cells. (A) FGF2-T-MAE-cell CM (bottom), but not MAE-cell CM (top), stimulates sprouting of MAE-cell aggregates in fibrin gel. This assay was used to follow the purification of FGF2-T-MAE-cell CM by cation exchange (B) and heparin-Sepharose (C) chromatography (horizontal bar, pooled bioactive fractions; diagonal dashed lines, NaCl gradient), and by reverse-phase HPLC (D). Bioactive HPLC peaks (*,**) were probed with anti-Drm/gremlin antibodies in a Western blot (D, inset) and identified by MALDI-ToF peptide mass fingerprinting (peak * in panel E; peak **, not shown). (F) Amino acid sequence of Drm/gremlin. Tryptic (underlined) or CNBr (italic) digestion peptides were sequenced by nano-ESI-MS/MS. N-glycosylation (N) and Ser-phosphorylation (S) sites are highlighted.