No abstract

The concentrations of free amino acids and several related compounds in rabbit cornea and its stroma and epithelium were determined by ion exchange chromatography and compared with corresponding values in aqueous humor. The major ninhydrin reacting compounds in the cornea were found to be taurine, asparagine and glutamine, glycine, alanine and glutamic acid, the concentration of taurine being the highest of all substances determined. While in most instances stroma was found to contain the major portion of the compounds present in the cornea, nearly 70% of both β-alanine and glutathione were present in the epithelium. Except for the basic amino acids arginine, lysine and ornithine and the two neutral compounds methionine and hydroxyproline, the concentration of every free amino acid in the corneal epithelium was found to be higher than in the stroma and aqueous humor. The ratio of the concentration in the corneal epithelium to that in the aqueous was highest for acidic, lowest for basic and intermediate for neutral amino acids, an observation similar to that made previously in the lens. It is concluded that the high concentration gradients between the corneal epithelium and aqueous humor are maintained by active transport mechanisms. The role of corneal epithelium in the turnover rate of amino acids in the aqueous humor is discussed.