An aqueous solution of a pigmented glucoside associated with human lens protein, 2-amino-3-hydroxyacetophenone-O-beta-D-glucoside (AHA-Glc), was irradiated with near UV-light. The near UV-irradiated glucoside was shown to generate a much lower level of active species of molecular oxygen as compared to the level of the active species generated from the irradiated aglycon, 2-amino-3-hydroxyacetophenone (AHA). This result suggests that the glycon of the glucoside is functioning as a scavenger for active oxygen generated from the aglycon of the irradiated glucoside. Superoxide dismutase (SOD) was shown to remove a large portion of the active oxygen generated from the irradiated AHA, so the bulk of the active species generated is assumed to be superoxide anion. The small portion of active oxygen remains after removal of superoxide anion may include singlet oxygen. The photooxidation of tryptophan residues of calf alpha-crystallin irradiated with near UV-light in the presence of AHA-Glc or AHA was investigated to confirm the role that the glycon plays in diminution of the active species of oxygen generated through the photosensitized aglycon of the glucoside. A decrease with time in the fluorescence intensity of the tryptophan residues irradiated with AHA-Glc was shown to be much slower as compared to the time-dependent decrease with AHA, indicating that the photooxidation proceeds with an increase in accumulation of active oxygen generated through the aglycon and that the glycon of the glucoside deactivates the active species as it is formed in the photodynamic process. Similar effects have also been observed in calf lens crystallin irradiated with either 3-hydroxykynurenine-O-beta-D-glucoside (HKN-Glc) or 3-hydroxykynurenine (HKN). Furthermore, effects of near UV-irradiation on calf lens soluble protein in the presence of AHA-Glc or AHA were studied by monitoring changes in the SDS-PAGE profile of the irradiated protein. Near UV-irradiation with AHA-Glc was shown to bring about a slight change in cross-linking of the polypeptides, while irradiation with AHA was shown to give rise to a significant increase in cross-linking of the polypeptides. In conclusion, pigmented glucoside associated with human lens protein is not only a photosensitizer for near UV-light but also an anti-photooxidant to deactivate active oxygen formed through the in situ photosensitizer, in order that photooxidative insults to lens proteins may be minimized during aging.