Nonenzymatic glycation of human lens crystallin. Effect of aging and diabetes mellitus.

We have examined the nonenzy- matic glycation' of human lens crystallin, an extremely long-lived protein, from 16 normal human ocular lenses 0.2-99 yr of age, and from 11 diabetic lenses 52-82-yr- old.The glucitol-lysine (Glc-Lys)2 content of soluble and insoluble crystallin was determined after reduction with 3H-borohydride followed by acid hydrolysis, boronic acid affinity chromatography, and high pressure cation exchange chromatography.Normal lens crystallin, sol- uble and insoluble, had 0.028±0.011nanomoles Glc- Lys per nanomole crystallin monomer.Soluble and insoluble crystallins had equivalent levels of glycation.The content of Glc-Lys in normal lens crystallin in- creased with age in a linear fashion.Thus, the nonenzymatic glycation of nondiabetic lens crystallin may be regarded as a biological clock.The diabetic lens crystallin samples (n = 11) had a higher content of Glc-Lys Receivedfor publication 9 April 1984.1.The Joint Commission on Biochemical Nomenclature of the International Union of Biochemistry (IUB) and the International Union of Pure and Applied Chemistry (IUPAC) suggests the term "glycation" rather than "glycosylation" or "glucosylation" for the nonenzymatic reaction between glucose or other sugars, and free amino groups of proteins (1).2. The borohydride-reduced product of lysino-l-deoxyfructose (glucosyl- lysine) is a mixture of lysino-l-deoxysorbitol and lysino-l-deoxymannitol.The Durrum DC-6A cation exchange column does not separate these two epimers; they elute in one symmetrical peak.For simplicity, we refer to the mixture of these epimeric forms as glucitol-lysine throughout this paper.In like manner, the borohydride-reduced product of valyl- 1-deoxyfructose (glucosyl-valine) is a mixture of valyl-l-deoxysorbitol and valyl-l-deoxymannitol, which also elutes as one peak on our column and is called glucitol-valine.(0.070±0.034 nmol/nmol monomer).Over an age range comparable to that of the control samples, the diabetic crystallin samples contained about twice as much Glc- Lys.The Glc-Lys content of the diabetic lens crystallin samples did not increase with lens age.3.