Detection of glycated fetal human lens crystallins by concanavalin-A and aldehyde staining

The binding of the lectin Concanavalin-A (Con-A) to crystallins was investigated. For this purpose, human fetal and juvenile lens crystallins were isofocused and specifically stained brown for glycoproteins by the lectin Con-A, and purple by the periodic acid Schiff's reagent (PAS). In reference experiments protein bands were stained with Coomassie Blue for proteins. Since Con-A is a protein with glucose-specific receptors, the following crystallins, glycated with this sugar, were visualized after isoelectric focusing: HM-, beta L-, beta S- and gamma-crystallins, but not alpha L- and beta H-crystallins. Glycation increased significantly with fetal age. The crystallins themselves could also function as sugar receptors, because it was shown that they possessed also receptors for glucose, like Con-A. This crystallin receptor staining revealed beta L-, beta S-, gamma- but hardly HM-crystallins. The PAS, Con-A and receptor stainings gave in principle identical results. The glycoproteins Con-A, horseradish peroxidase and lentil lectins were used as positive controls.