Depending on the reaction conditions, peri-hydroxy substituted anthraquinones like 1,8-dihydroxyanthraquinone and 1,4-dihydroxyanthraquinone could be derivatized with ammonia, propylamine, isopropylamine, and a lysine derivative to yield a variety of imino and amino substitution and addition products.However, hypericin resisted such derivatization under a variety of reaction conditions.Therefore, the hypothesis that hypericin is bound to its apoprotein in photopigments via a Schiff base to the ε-amino group of a lysine residue or a terminal amino group seems to be rather unlikely. - Keywords.Hypericin; Stentor; Schiff base; Anthraquinone imines; Aminoanthraquinones.