Acidic peptides of the lens

Abstract

Calf lenses were disintegrated in an acid or alkaline buffer, and the solution was dialyzed. The diffusible compounds were fractionated by electrophoresis on cellulose powder, and on filter paper, followed by paper chromatography. Two ninhydrin-positive acidic fractions were examined in detail; both contained several peptides. Hydrolysis of one of these acidic fractions liberates [alpha]-amino-n-butyric acid, arising from a tripeptide containing also glutamic and glycine residues; the glutamic acid is N-terminal. The tripeptide ("ophthalmic acid") is present at a relatively high concentration, of the order of 20 mg/l00g of calf lens, but it was not detected in the liver or erythrocytes of the calf. The other acidic fraction contains peptides (other than glutathione) built up from glutamic acid, cystine (or cysteine) and glycine. Some of these peptides contain a strongly acidic group (so far unidentified), so that the molecule has zero net charge at pH 2. One of these peptides is a tripeptide containing an N-terminal glutamic acid residue.