Function of heparin and dextran sulfate for removing proteins
See here.

Histones are basic proteins (cationic, high pI) because they are required to interact with polyanionic DNA at physiological pH. Heparin and dextran are polyanions which form insoluble salts with the cationic histones.(Dextran is a polymer of glucose. In dextran sulphate it is derivatised with sulphonate groups creating a polyanionic material.)

Immobilised heparin is sometimes used as an affinity matrix for purification of DNA-binding proteins like transcription factors.