No abstract

UVA light causes inactivation of GR in human and fetal calf lenses under both anaerobic and aerobic conditions. This suggests that flavine adenine dinucleotide (FAD), the prosthetic group of GR, may be responsible for the enzyme's self-sensitizing properties. WS proteins from aged human lens generate reactive oxygen species (ROS) during UVA irradiation, which may be responsible for the inactivation of G3PD.

These data argue that UVA light can cause an oxidation of ascorbic acid in the absence of oxygen, due to the activation of the sensitizers present in aged human lens WI proteins. The oxidation products formed were the same as those seen in the presence of oxygen, and were rapidly incorporated into protein, apparently by Maillard-type chemistry. These data argue that ascorbate glycation can occur under the low oxygen levels thought to exist in the human lens nucleus in vivo.

The results show that the reduction of HL GR activity by UVA light was directly linked to the presence of FAD within the enzyme. That the irradiated GR showed de novo formed SH groups argues that UVA photolysis of GR leads to the reduction of the redox-active disulfide within the reaction center of the enzyme, making it inactive.