Biochemical model reactions for cataract research.

There are several experimental indications that cataract formation is induced and/or enhanced by activated oxygen species including hydrogen peroxide, superoxide radical anion, singlet oxygen and hydroxyl radical. These species can be generated chemically, enzymatically or photodynamically. Taking advantage of endogenous photodynamic compounds in isolated lens, aqueous humor or vitreous preparations in the presence of S-methyl-alpha-ketobutyric acid (KMB), ethylene formation can be monitored for at least 2 h of light-dependent KMB degradation. This reaction is extremely sensitive and can be inhibited by potassium iodide in low concentrations. This model reaction might be useful for studying possibly inhibiting substances or stimulating processes involved in cataract formation.