| Age-related cataract is the most common type of cataract. In recent years, many researchers believe: age-related cataract is a protein structural change disease, irreversible degeneration of the lens proteins and lens abnormalities of protein breakdown. In this study, we mainly discuss the relationship between the changes of proteins and enzymes in lens and age-related cataract.Dipeptidyl peptidase II (DPPII) is a system located in intracellular vesicles lysosomal protease, as a kind of exo peptidase. Its molecular weight on SDS-PAGE is about 60Kda, generally considered DPPII consists of two identical glycosylated protein chains through the combination of non-covalent bond (for the dimer), located upstream of catalytic domain leucine zipper for the enzyme catalytic activity and formation are necessary. Has now been confirmed DPPII widely distributed in various organs, tissues and cells, such as the brain, kidneys, eyes, reproductive organs, body fluids, blood cells and so on. The researchers speculated that DPPII involved in cell differentiation and prevent cell death process, and in the collagen fragments, muscle fiber proteins and short neuropeptides play a role in the degradation. Some academics have already proved DPPII exist in the normal cattle, mouse and human lens and cataract lens it has a high biochemical activity and immune activity. : Hui Zhang etc. observed immunohistochemically that DPPII distributed in the lens epithelium and the perinuclear region of lensfibers of control rats at all ages, and its immunological activityincreased in the lens of Shumiya cataract rats compared with thecontrol rats'. Rui Tian etc. through the establishment of D-galactose cataract in rat animal model and to detect DPPII in the D-galactose cataract in rat lens is higher than normal rat lens levels.Object:In order to find the role of DPPII played during cataract formation,we choosed hunman lens as our study targets, and detect the expression of dipeptidyl peptidase II in human lens of age-related cataract.Methods:Firstly,Western-blotting was used to examine the content of DPPII in human lens of age-related cataract. Then, enzyme activity of DPPII was determined by directly monitoring the absorbrance with UV-2500PC at 525nm 37℃, according to the enzyme can removes the dipeptides from the special substrate (Lys-Ala-pNA).Results:The results of Western-blotting for examining the content of DPPII indicate that the content of DPPII in human lens increased with lens nuclear hardness increased. The results of enzyme activity of DPPII indicate that the enzyme activity of DPPII in human lenses increased with lens nuclear hardness increased.Conclusion: Based on these results, the expression changes of DPPII in human lenses with lens nuclear hardness increased,maybe involved in the changes of crystallin. For example:the content ofαB-crystallin can be cleaved off from N-terminus and shown the feature of post-translational modification to dereased in soluble components but increased in insoluble components with the increase in turbidity as the lens.αB-crystallin has It also be identified that it. When the concentration of Ca2+ increased in lens, some endo-peptidases , such as calpains etc , are activated by Ca2+ in lens.So that some lens protein was firstly degraded into peptide fragments. The N-terminal specifical amino acid sequences of these polypeptide fragments, such as : Lys–Ala,Lys–Pro, Arg–Pro,etc, are revealed , and then are recognized and hydrolyzed or post-translational modified by DPPII.All these change the original structure and sequence of crystal protein or peptides. Thus,αA-,αB-crystallin becomes insoluble, giving rise to transparency changes of lens. It demonstrates that DPPII may act an important function in the formation and the aggravation of age-related cataract. We conclude that DPPII play an important role in hydrolyzing crystallin or modifying post-translation,in the process of lens aging or opacification.
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