Activators and inhibitors of lens aldose reductase.

Aldose reductase in a highly purified state is unstable. It requires the presence of thiol groups to maintain it in an active form. The enzyme apparently exists in 3 forms, only one of which is active. Tetramethylene glutaric acid (TMG) is an effective aldose reductase inhibitor. However, a relatively high level of TMG is needed to depress dulcitol synthesis in the lens incubated in a galactose containing medium. TPN+, a product of the reaction, also inhibits the enzyme. The action of these inhibitors appears to transform the active into inactive enzyme.