Evidence for lens oxoprolinase, an enzyme of the gamma-glutamyl cycle.

The presence of oxoprolinase, an enzyme of the gamma-glutamyl cycle, not previously reported in the lens was demonstrated by organ-culture technique and from a study of the partially purified enzyme. The evidence for oxoprolinase in intact rabbit lens is based on the following: (1) [14C]-labeled oxoproline is utilized by the lens giving rise to labeled CO2, (2) [14C]-oxoproline is converted to glutamic acid, which is subsequently incorporated into glutathione, (3) formation of labeled glutamic acid and CO2 from [14C]-oxoproline is effectively blocked by a structural analog of the compound L-2-imidazolidone-4-carboxylic acid, a known inhibitor of oxoprolinase. The enzyme was partially purified from bovine lens capsule epithelium and certain of its properties were examined. Ocular lens was also found to contain significant amounts of oxoproline, an intermediate of the gamma-glutamyl cycle.