SDS-PAGE of proteoglycans isolated from the supernatant of the immature erythroid progenitor cell line HEL. HS proteoglycans from HEL cells were metabolically radiolabeled with [³⁵S]-sulfate. In addition, core proteins were metabolically labeled by a mixture of [³⁵S]-methionine [³⁵S]-cysteine and a [¹⁴C]-labeled amino acid mixture. Proteoglycans isolated from the supernatant of the immature erythroid progenitor cell line HEL were digested by chondroitinases AC/ABC (A), heparinase/heparitinase (H), or a combination of chondroitinases AC/ABC and heparinase/heparitinase (A/H) and submitted to SDS-PAGE on a 4% to 15% gel. N, native sample.