Proteins human lens

In addition to a-l-PI, there are other examples of the presence of Met(O) residues in proteins isolated from biological material. Proteins found in lens tissue are particularly susceptible to photooxidation and because of the long half-lives of these proteins, any oxidation could be especially detrimental. In this tissue, protein synthesis is localized to the outer region of the tissue and most proteins are stable for the life of the tissue - ". It is thus somewhat surprising that not only is there no Met(O) residues in the young normal human lens but even in the old normal human lens only a small amount of Met(O) residues is found . However, in the cataractous lens as much as 65% of the Met residues of the lens proteins are found in the form of Met(0) . Whether this increase in Met(O) content in these proteins is a cause or a result of the cataracts is not known. In order to determine whether the high content of Met(O) in the cataractous lens is related to a decreased activity of Met(0)-peptide reductase, the level of this enzyme was determined in normal and cataractous lenses. It can be seen from Table 9 that there are no significant differences between the levels of Met(0)-peptide reductase in normal and cataractous lenses. In spite of these results, however, it is still possible that the Met(0)-peptide... 

Augusteyn, R.C. (1981). Protein modification in cataract possible oxidative mechanisms. In Mechanisms of Cataract Formation in the Human Lens (ed. G. Duncan) pp. 71-115, Academic Press, London. 

In the aging human lens, and particularly during cataract formation, protein aggregation (81), decreased protein solubility... 

P. S. Padayatti, A. S. Ng, K. Uchida, M. A. Glomb, and R. H. Nagaraj, Argpyrimidine, a blue fluorophore in human lens proteins High levels in brunescent cataractous lenses, Invest. Ophthal. Visual Sci., 2001, 42, 1299-1304. 

E. B. Frye, T. P. Degenhardt, S. R. Thorpe, and J. W. Baynes, Role of the Maillard reaction in aging tissue proteins Advanced glycation end product-dependent increase in imi-dazolium cross-links in human lens, J. Biol. Chem., 1998, 273, 18714—18719. 

W8. Wells-Knecht, M. C., Huggins, T. G., Dyer, D. G., Thorpe, S. R., and Baynes, J. W., Oxidized amino acids in lens protein with age. Measurement of o-tyrosine and dityrosine in the aging human lens. J. Biol Chem 268, 12348-12352(1993). 

Paisey, R., Valles, V., Arredondo, G., Wong, B., and Lozano-Castaneda, O., Measurement of glycosylated haemoglobin at high altitudes. Diabetologia 22, 493 (1982). Pande, A., Gamer, W. H., and Spector, A., Clucosylation of human lens protein and cataractogenesis. Biochem. Biophys. Res. Common. 89, 1260-1266 (1979). 

Cataractogenesis. Cataractogenesis has been noted in the human lens, due to PTM of lens protein aP-crystallin by carbamylation and acetylation at Lys-92 [45]. 

Lapko V N, Smith D L, Smith J B (2001). In vivo carbamylation and acetylation of water-soluble human lens alphaB-crystallin lysine 92. Protein Sci. 10 1130-1136. 

Lou ME, Dickerson JE. Protein-thiol mixed disulfides in human lens. Exp Eye Res 1992 55 889-896. 

Dillon, J. Spector, A. 8c Nakanishi, K. 1976. Identification of 13-carbolines isolated from fluorescent human lens proteins. 

Examination of proteins for D-glucosyl-L-lysine in normal human lens, senile and diabetic cataracts shows that D-glucosylation does not appear to be a primary factor in cataract formation. 

Nagaraj, R. H., Sell, D. R., Prabhakaram, M., and Ortwerth, B. J., 1991, High correlation between pentosidine protein cross-links and pigmentation implicates ascorbate oxidation in human lens senescence and cataractogenesis, Proc. Natl. Acad. Sci. USA 88 10257-10261. 

Bours, J., Wegener, A., Hofmann, D., Fodisch, H.J., Hockwin, O. Protein profiles of microsections of the fetal and adult human lens during development and ageing. 

A. Kamei, Glycation and insolubility of human lens proteins. Chem. Pharm. Bull. 40 2787(1992). 

H.A. Kramps, H.J. Hoenders and J. Wollensak, Protein changes in the human lens during... 

M.S. Swamy, A. Abraham and E.C. Abraham, Glycation of human lens proteins Preferential... 

The above data unequivocally established the fact that protein carbonyls stemming from metal catalyzed oxidation are present in the aging human lens, and that these modifications are increased in presence of diabetes. The mechanistic studies with rabbit lenses exposed to hyperbaric oxygen confirm the critical role of oxygen in the formation of allysine. 

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