Jacalin (Artocarpus integrifolia
agglutinin) specifically recognizes the
tumor-associated T-antigenic
disaccharide structure, Gal beta13GalNAc.
Porphyrins and their derivatives are currently used as
photosensitizers in
photodynamic therapy to treat malignant
tumors. In this study, the interaction of several free base
porphyrins and their
metal derivatives with
jacalin is investigated by absorption and fluorescence spectroscopy. Each
lectin subunit was found to bind one
porphyrin molecule and the association constants were estimated to be in the range of 2.4 x 10(3) M(-1) to 1.3 x 10(5) M(-1) at room temperature for the interaction of different
porphyrins with
jacalin. These values are in the same range as those obtained for the interaction of
monosaccharides to
jacalin. Both free
lectin and
lectin saturated with the specific saccharide were found to bind different
porphyrins with comparable binding strength indicating that
porphyrin binding takes place at a site different from the
sugar binding site. Further, both anionic and cationic
porphyrins were found to interact with the
lectin with comparable affinity, clearly indicating that the charge on the
porphyrin does not play any role in the binding process and that most likely the interaction is mediated by hydrophobic forces. These results suggest that
jacalin and other
lectins may potentially be useful for targeted delivery of
porphyrins to
tumor tissues in
photodynamic therapy.