Scientists have examined the nonenzymatic 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) content of soluble and insoluble crystallin was determined after reduction with H-borohydride followed by acid hydrolysis, boronic acid affinity chromatography, and high pressure cation exchange chromatography.
Normal lens crystallin, soluble and insoluble, had 0.028 ± 0.011 nanomoles Glc-Lys per nanomole crystallin monomer.
Soluble and insoluble crystallins had equivalent levels of glycation.
The content of Glc-Lys in normal lens crystallin increased 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 (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.