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Ma Y, Zhou Q, Zhao P, Lv X, Gong C, Gao J, Liu J. Effect of transferrin glycation induced by high glucose on HK-2 cells in vitro. Front Endocrinol (Lausanne) 2022; 13:1009507. [PMID: 36778593 PMCID: PMC9909336 DOI: 10.3389/fendo.2022.1009507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 12/19/2022] [Indexed: 01/27/2023] Open
Abstract
BACKGROUND AND OBJECTIVE Glycation is a common post-transcriptional modification of proteins. Previous studies have shown that advanced glycation end modified transferrin (AGE-Tf) levels in diabetic rat kidney tissues were increased; however, its role in diabetic nephropathy remains unclear. In this study, differences in glycation degree and Tf sites induced by differing high glucose concentrations in vitro and the effect on total iron binding capacity (TIBC) were observed. Moreover, the effect of AGE-Tf on human renal tubular epithelial cells (HK-2) was investigated. METHODS In vitro Tf was incubated with increasing glucose concentrations (0 mM, 5.6 mM, 11.1 mM, 33.3 mM, 100 mM, 500 mM, and 1,000 mM) for AGE-Tf. Differences in AGE-Tf glycation degree and TIBC level were analyzed via colorimetric method. The AGE-Tf glycation sites were identified with LC-MS/MS. HK-2 cells were treated with AGE-Tf prepared with different glucose concentrations (33.3 mM and 500 mM) in vitro. The effects of AGE-Tf on HK-2 cell viability, proliferation, oxidative stress index, and Tf receptor expression levels were then observed. RESULTS With increasing glucose concentrations (100 mM, 500 mM, and 1,000 mM) in vitro, Tf glycation degree was significantly increased. The TIBC levels of AGE-Tf were decreased significantly with increasing glucose concentrations (33.3 mM, 100 mM, 500 mM, and 1,000 mM). Four glycated modification sites in Tf and 17 glycated modification sites were detected in AGE-Tf (500 mM) by LC-MS/MS. The structural types of AGEs were CML, G-H1, FL-1H2O, FL, and MG-H1. No significant differences were found in the survival rate of HK-2 cells among the AGE-Tf (500 mM), AGE-Tf (33.3 mM), and Tf groups (all p > 0.05). The apoptosis rate of HK-2 cells in the AGE-Tf (500 mM) group was significantly higher than that in the AGE-Tf (33.3 mM) group. Additionally, both of them were significantly higher than that in the Tf group (both p < 0.05). The MDA levels of HK-2 cells in the AGE-Tf (500 mM) and AGE-Tf (33.3 mM) groups were higher than that in the Tf group, but not significantly (both p > 0.05). The T-AOC level of HK-2 in the AGE-Tf (500 mM) group was significantly lower than that in the AGE-Tf (33.3 mM) and Tf groups (both p < 0.001). The GSH level of HK-2 cells in the AGE-Tf (500 mM) group was significantly lower than that in the Tf group (p < 0.05). The expression level of TfR in the AGE-Tf (500 mM) group was also significantly lower than that in the Tf group (p < 0.05). CONCLUSION The degree and sites of Tf glycation were increased in vitro secondary to high-glucose exposure; however, the binding ability of Tf to iron decreased gradually. After HK-2 was stimulated by AGE-Tf in vitro, the apoptosis of cells was increased, antioxidant capacity was decreased, and TfR expression levels were downregulated.
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Affiliation(s)
- Yanqi Ma
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, China
| | - Qikai Zhou
- Tianjin Normal University, Tianjin, China
| | - Pingping Zhao
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, China
| | - Xiaoyu Lv
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, China
| | - Caixia Gong
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, China
| | - Jie Gao
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, China
| | - Jingfang Liu
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, China
- Department of Endocrinology, The First Hospital of Lanzhou University, Lanzhou, Gansu, China
- *Correspondence: Jingfang Liu,
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Ma Y, Cai J, Wang Y, Liu J, Fu S. Non-Enzymatic Glycation of Transferrin and Diabetes Mellitus. Diabetes Metab Syndr Obes 2021; 14:2539-2548. [PMID: 34135606 PMCID: PMC8197663 DOI: 10.2147/dmso.s304796] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 05/10/2021] [Indexed: 11/23/2022] Open
Abstract
Diabetes is a metabolic disease characterized by high blood sugar. Its complications may damage multiple organs, such as eyes, kidneys, heart, blood vessels, and nerves, severely threatening human health. Transferrin (Tf) is a major iron transport protein in the body. Recent studies have shown that the degree of non-enzymatic glycated modification of Tf is increased in diabetic patients, and glycated Tf is closely related to the occurrence and development of diabetes and diabetic complications. However, the molecular mechanisms underlying this glycated modification in diabetes and diabetic complications are still unclear. It is speculated that the mechanism may be that glycated modification reduces the binding ability of Tf and its receptor TfR, followed by excessive iron accumulation in the body. Iron overload in the body may further lead to the death of pancreatic beta cells and insulin resistance by increasing oxidative stress, inducing iron death, interfering with the insulin signaling pathway, and causing autophagy deficiency. In addition, non-enzymatic glycation affects the binding of Tf with chromium and reduces the ability of Tf to transport chromium into tissues, resulting in a decrease in the levels of chromium in tissues and ultimately affecting the sensitivity of tissues to insulin. In diabetic patients, the concentrations of glycated Tf in serum were significantly correlated with those of fructosamine.Tf has a shorter half-life, and not affected by anemia or hypoalbuminemia and less negative charge under physiological conditions, while glycated modification could not change the isoelectric point of Tf, which easily passes through the negatively charged basement membrane of the glomerulus. Therefore, compared to glucosamine, HbA1C, etc., glycated Tf may be a future biomarker for evaluating short-term glycemic control and early renal damage in diabetic patients.
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Affiliation(s)
- Yanqi Ma
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, People’s Republic of China
| | - Jing Cai
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, People’s Republic of China
| | - Ying Wang
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, People’s Republic of China
| | - Jingfang Liu
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, People’s Republic of China
- Department of Endocrinology,The First Hospital of Lanzhou University, Lanzhou, Gansu, People’s Republic of China
- Correspondence: Jingfang Liu Department of Endocrinology, The FirstHospital of Lanzhou University, 1 Donggang West Road, Lanzhou, Gansu, 730000, People’s Republic of ChinaTel +86-931-8356242 Email
| | - Songbo Fu
- The First Clinical Medical College, Lanzhou University, Lanzhou, Gansu, People’s Republic of China
- Department of Endocrinology,The First Hospital of Lanzhou University, Lanzhou, Gansu, People’s Republic of China
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Ramalho JS, Marques C, Pereira PC, Mota MC. Role of Glycation in Human Lens Protein Structure Change. Eur J Ophthalmol 2018; 6:155-61. [PMID: 8823589 DOI: 10.1177/112067219600600211] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
PURPOSE Protein glycation may be involved in cataract development, by altering protein structure, particularly amino acid composition, and formation of fluorophores through a Maillard reaction. This study was designed to evaluate major changes in early and advanced (fluorescent) glycation products, with special emphasis on glycation-induced changes in amino acid composition of lens proteins. METHODS We analyzed 50 human cataractous lenses (25 diabetic and 25 non-diabetic). Glycated proteins were isolated by affinity chromatography. Glycated and non-glycated proteins were separated by molecular sieve chromatography and further analyzed by RP-HPLC to establish the amino acid content. Early glycation levels were determined as furosine content and advanced glycation products were quantified by the characteristic fluorescence. RESULTS Specific lens fractions (HMW and LMW) present significant differences in fluorescence levels between glycated and non-glycated proteins, specially in cataractous lenses from diabetic patients in which all proteins analyzed presented higher glycation levels than in non-diabetic patients. The amino and analysis of glycated proteins also revealed some important differences in specific basic residues (namely Lys, Arg and His) compared to the non-glycated fraction. CONCLUSIONS The results suggest that protein glycation may be involved in changes in amino acid composition and fluorophore formation. This process may well account for the increased risk factor that diabetes represents for cataract development.
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Affiliation(s)
- J S Ramalho
- Department of Ophthalmology and Visual Sciences, University of Coimbra, Portugal
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Kaufmann M, Haase PT, Mügge C, Kroh LW. Milieu dependence of isomeric composition of D-arabino-hexo-2-ulose in aqueous solution determined by high-resolution NMR spectroscopy. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2013; 61:10220-10224. [PMID: 23822666 DOI: 10.1021/jf305302e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In this study, high-resolution (1)H NMR spectroscopy (600.03 MHz) and (13)C NMR spectroscopy (150.89 MHz) were used to elucidate the structures of equilibrating d-arabino-hexo-2-ulose (GLUC) (1) isomers in aqueous solution. Four isomers were formed from the investigated ketohexose, and their equilibrium is dependent on the pH value and temperature. Only hydrated GLUC (1) isomers were identified. The (2)C5-β-2,6-pyranoid and the β-2,5-furanoid GLUC (1) isomer were exclusively formed in aqueous solution. Thus, (4)C1-1,5-pyranoid isomers are predominating in the crystalline state. An increase in solution pH or temperature led to a pairwise conversion of configurative information. Thus, changing the measurement conditions permits control over the equilibrium's characteristic. Furthermore, all GLUC (1) isomers showed comparable reaction behavior regarding pH- and temperature-dependent degradation reactions.
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Affiliation(s)
- Martin Kaufmann
- Department of Food Chemistry and Food Analysis, Berlin Institute of Technology , Gustav-Meyer-Allee 25, TIB 4/3-1, D-13355 Berlin, Germany
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Kaufmann M, Haase PT, Mügge C, Kroh LW. Milieu dependence of isomeric composition of 1-deoxy-d-erythro-hexo-2,3-diulose in aqueous solution determined by high-resolution NMR spectroscopy. Carbohydr Res 2012; 364:15-21. [DOI: 10.1016/j.carres.2012.10.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 10/11/2012] [Accepted: 10/13/2012] [Indexed: 10/27/2022]
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Rowe N, Mitchell P, Cumming RG, Wans JJ. Diabetes, fasting blood glucose and age-related cataract: the Blue Mountains Eye Study. Ophthalmic Epidemiol 2009. [DOI: 10.1076/0928-6586(200006)721-zft103] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Shyadehi AZ, Harding JJ. Protective effects of ibuprofen and its major metabolites against in vitro inactivation of catalase and fumarase: relevance to cataract. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1587:31-5. [PMID: 12009421 DOI: 10.1016/s0925-4439(02)00049-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Ibuprofen and its major metabolites were incubated with catalase and fumarase, in the presence of protein-modifying biomolecules, to explore the mode of action of ibuprofen in protection against cataract. Both 2 and 10 mM ibuprofen/metabolites protected catalase against fructose-, cyanate- and prednisolone-induced inactivation; the carboxy-metabolite gave the highest protection (31%). The 2 mM ibuprofen/metabolites protected fumarase against fructose- and cyanate-induced inactivation by up to 26%, but had no effect on prednisolone-induced inactivation. Ibuprofen/metabolites did not bind to catalase or fumarase. They penetrated into the lens in vitro. When in the lens, the metabolites may reduce the risk of cataract by protecting lenticular enzymes.
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Affiliation(s)
- Akbar Z Shyadehi
- Nuffield Laboratory of Ophthalmology, University of Oxford, Walton Street, OX2 6AW, UK.
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Thampi P, Zarina S, Abraham EC. alpha-Crystallin chaperone function in diabetic rat and human lenses. Mol Cell Biochem 2002; 229:113-8. [PMID: 11936835 DOI: 10.1023/a:1017980713089] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This study focussed on the effect of diabetes on the chaperone function of alpha-crystallin. The authors relied on diabetic rats with a wide range of plasma glucose levels and non-diabetic control rats to establish a possible relationship between severity of diabetes and alpha-crystallin chaperone activity. In addition, 52-56 and 63-69 year-old diabetic and non-diabetic human lenses were used to show whether diabetes affects alpha-crystallin chaperone activity in human lenses. Correlation between plasma glucose levels and loss of chaperone activity of the alphaL-crystallin fraction in diabetic rats indicated good correlation. The glycemic threshold, reported before for cataract development in diabetic rats, seems to be valid for the chaperone activity loss as well. Analysis of the human lens alphaL-crystallin showed lower chaperone activity in all the diabetic lenses than in the age-matched control lenses. In the 63-69 age group, the loss in chaperone activity due to diabetes was significantly larger than in the 52-56 age group suggesting a dominant effect of duration of diabetes.
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Affiliation(s)
- Prajitha Thampi
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205, USA
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Kamińska A, Kowalska M. A study of the lens crystallin's photodegradation in the presence of β-carotene. Polym Degrad Stab 1999. [DOI: 10.1016/s0141-3910(99)00046-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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11
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Linetsky M, James HL, Ortwerth BJ. Spontaneous generation of superoxide anion by human lens proteins and by calf lens proteins ascorbylated in vitro. Exp Eye Res 1999; 69:239-48. [PMID: 10433859 DOI: 10.1006/exer.1999.0710] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The proteins isolated from aged human lenses and brunescent cataracts exhibit extensive disulfide bond formation. Diabetic rat lenses similarly contain disulfide-bonded protein aggregates. These observations are consistent with the known link between diabetes, glycation and oxidative damage, and suggest a role for reactive oxygen species (ROS) in this process. To assess whether the glycation-related modifications in human lens proteins spontaneously generate ROS, superoxide anion formation was measured using both cataractous lens proteins and calf lens proteins glycated in vitro with ascorbic acid (ascorbylated). The water-insoluble fraction from aged normal human lenses generated 0.3-0.6 nmol superoxide h(-1)mg protein(-1), whereas the activity increased to 0.5-1.8 nmol h(-1)mg protein(-1)with the WI fraction from brunescent cataracts, and 2.3 nmol h(-1)mg protein(-1)with calf lens proteins ascorbylated for 4 weeks in vitro. The activity in the human lens proteins was observed in both the water-soluble and water-insoluble fractions, and was completely dependent upon the presence of oxygen. The pH optimum curve for superoxide formation increased from pH 6.5 to 10 with both the cataract and ascorbylated proteins. The superoxide-generating activity in human lens was completely bound to a boronate affinity column, but only partially bound with the ascorbylated proteins. The superoxide anion produced by a 5 m m solution of purified N(epsilon)-fructosyl-lysine was barely detectable, and therefore, could not account for the superoxide formed by any of the lens protein preparations. Also, superoxide formation increased 10-fold at pH 8.8 with fructosyl-lysine, but only 1.3-1.8-fold with human lens proteins. The addition of copper-stimulated superoxide formation with glycated bovine serum albumin, but no stimulation was seen with cataractous proteins. Assays of specific compounds showed that catechol, hydroquinone, 3-OH kynurenine and 3-OH anthranylic acid exhibited the greatest activity for superoxide generation, but had a very short halflife. 2,3-Dihydroxypyridine and 4,5 dihydroxynaphthalene were one and two orders of magnitude less reactive. In long-term incubations at 37 degrees, cataractous proteins retained the potential to produce superoxide anion, losing only half of the initial activity after 6-7 days. Therefore, the water-insoluble fraction from aged human lenses and dark brown cataracts are potentially capable of generating >100 nmol mg protein(-1)and >170 nmol mg protein(-1)of superoxide anion respectively, likely due to the presence of advanced glycation endproducts in human lens proteins. This spontaneous generation of superoxide anion in vivo could account for a major portion of the oxidation of sulfur amino acids seen during aging and cataract formation.
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Affiliation(s)
- M Linetsky
- Mason Eye Institute, University of Missouri, Columbia, MO, 65212, USA
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Lee KW, Simpson G, Ortwerth B. A systematic approach to evaluate the modification of lens proteins by glycation-induced crosslinking. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1453:141-51. [PMID: 9989254 DOI: 10.1016/s0925-4439(98)00097-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
To systematically evaluate the modification of lens proteins by aldose and dicarbonyl sugars during the glycation process, the sugar-dependent incorporation of Lys and Arg, SDS-PAGE profile, amino acid analysis, and fluorophore formation (excitation 370 nm/emission 440 nm) were determined. Reaction mixtures with glycolaldehyde, glyceraldehyde, threose and 3-deoxythreosone showed the greatest extent of Lys crosslinking and fluorescence formation. An increase in fluorescence intensity, but a decrease in Lys and Arg crosslinking, was found with glyoxal, methylglyoxal, hydroxypyruvaldehyde and threosone. In addition glyoxal, methylglyoxal and hydroxypyruvaldehyde caused the specific loss of Arg residues in lens proteins. Reaction mixtures with xylose, xylosone, glucose, glucosone and 3-deoxyglucosone exhibited the least protein modifications; however, incubation with 3-deoxyxylosone resulted in extensive loss of Lys and Arg residues, a higher extent of Lys or Arg crosslinking and significant fluorophore formation. Each sugar exhibited unique characteristics in the modification of lens proteins by glycation. To validly compare the protein modifications occurring during glycation reactions, a systematic approach was employed to evaluate the potential role of aldose and dicarbonyl sugars in protein modification.
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Affiliation(s)
- K W Lee
- Mason Eye Institute, University of Missouri, School of Medicine, Columbia 65212, USA
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Lee KW, Mossine V, Ortwerth BJ. The relative ability of glucose and ascorbate to glycate and crosslink lens proteins in vitro. off. Exp Eye Res 1998; 67:95-104. [PMID: 9702182 DOI: 10.1006/exer.1998.0500] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nonenzymatic glycation by glucose and/or ascorbate leads to the formation of advanced glycation end products (AGEs), which are thought to be a critical element in lens protein aging and cataract formation. The relative participation of these two glycating agents was evaluated in vitro. The incubation of 100 mM [U-14C]-D-glucose and 10 mM [U-14C]-L-ascorbate with lens proteins resulted in an increasing incorporation over 3 weeks, reaching a maximum of 100 nMol mg-1 protein and 160 nMol mg-1 protein with ascorbate. Glycation was proportional to carbohydrate concentration with both reagents, however ascorbate was 18-fold more reactive with lens proteins than glucose. Protein crosslinking was not obvious with 250 mM glucose as measured by SDS-PAGE, however, ascorbate caused extensive crosslinking even at 3.0 mM. The sugar-dependent incorporation of N alpha-formyl-[U-14C]-L-lysine ([U-14C]Nfl) into proteins, gave values of 1.5 nMol mg-1 protein after 3 weeks with 100 mM glucose compared to 11 nMol mg-1 protein with 10 mM ascorbate. On a molar basis, ascorbate was 70-fold more active than glucose and 100-fold more active than fructose in the crosslinking assay. N alpha-formyl-N epsilon-fructosyllysine (1.0 mM) dissociated to cause the incorporation of 1.2 nMol of [U-14C]NfL, but 1.0 mM 3-deoxyglucosone, the putative active dissociation product of fructosyl-lysine, produced only 1.5 nMol mg-1 protein of crosslinks. The chelator, DTPA, had little or no effect on crosslinking in our assay except at the highest carbohydrate level. These data argue that glucose crosslinking can be shown in vitro with lens proteins, however, it does not proceed significantly via 3-deoxyglucosone, and does not require transition metal ion-mediated oxidation to occur. Quantitatively, however, it is almost two orders of magnitude less than the crosslinking by ascorbate oxidation products in vitro.
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Affiliation(s)
- K W Lee
- Mason Institute of Ophthalmology, University of Missouri, Columbia 65212, USA
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Kappler F, Su B, Szwergold BS, Randall WC, Brown TR. Identification of galactitol 2-phosphate and galactitol 3-phosphate in the lens of galactose-fed rats. Metabolism 1995; 44:1527-31. [PMID: 8786718 DOI: 10.1016/0026-0495(95)90069-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Production of unusual phosphorylated metabolites in the lens is one of several changes caused by hyperglycemia. Sorbitol 3-phosphate (Sor-3P) and fructose 3-phosphate (Fru-3P) are two such compounds identified in the diabetic lens, and galactitol 2-phosphate (Gal-2P) and galactitol 3-phosphate (Gal-3P) are identified here in the galactosemic lens. These new compounds are the first example of galactitol metabolism in mammalian tissue other than liver. Sor-3P and Fru-3P are also present in the galactosemic lens, apparently synthesized directly from their precursors, sorbitol and fructose, which are elevated in the lens due to increased flux of glucose through the aldose reductase (AR) pathway. The NADPH necessary to support this increased flux is derived from activation of the hexose monophosphate shunt (HMPS), which is clearly demonstrated by a large increase in the concentration of sedoheptulose 7-phosphate (Sed-7P), a HMPS-specific metabolite. Additionally, during 3 weeks of galactose feeding, there is a dramatic increase in lenticular concentrations of galactitol, sorbitol, galactose, and fructose and a sharp decrease in inositol. Glucose remains unchanged. A precipitous loss of both phosphorylated and nonphosphorylated metabolites occurs after 3 weeks, possibly due to lens rupture.
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Affiliation(s)
- F Kappler
- Department of Nuclear Magnetic Resonance and Medical Spectroscopy, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
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Mota MC, Carvalho P, Ramalho JS, Cardoso E, Gaspar AM, Abreu G. Protein glycation and in vivo distribution of human lens fluorescence. Int Ophthalmol 1995; 18:187-93. [PMID: 7797380 DOI: 10.1007/bf00951795] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Glycated proteins formed by the Maillard reaction were measured by furosine determination in human normal lenses and in senile and diabetic cataracts. Furosine, an hydrolysis product of fructose-lysine adduct formed in the early stages of the Maillard reaction, was measured by high performance liquid chromatography (HPLC). Furosine levels in diabetic cataracts were found to be 3 to 4 times higher than those observed for senile cataracts. The increased glycation levels both in cortex and nucleus were related to the increase of fluorescence determined in vitro by fluorometry and in vivo by Scheimpflug photography. Lens proteins were incubated with glucose and it has been demonstrated that protein glycation occurred parallel with the increase in concentration of fluorescent chromophores that present similar characteristics as those observed in vivo. The results indicate that protein insolubilization seemed to involve preferentially glycated proteins and at least in diabetic cataracts, the process seems to be initiated in the cortical region.
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Affiliation(s)
- M C Mota
- Center for Ophthalmology, University of Coimbra, Portugal
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Lal S, Szwergold B, Kappler F, Brown T. Detection of fructose-3-phosphokinase activity in intact mammalian lenses by 31P NMR spectroscopy. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53023-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Ortwerth BJ, Slight SH, Prabhakaram M, Sun Y, Smith JB. Site-specific glycation of lens crystallins by ascorbic acid. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1117:207-15. [PMID: 1525182 DOI: 10.1016/0304-4165(92)90081-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The oxidation of ascorbic acid leads to the formation of several compounds which are capable of reacting with protein amino groups via a Maillard reaction. Radioactivity from [1-14C]ascorbic acid was linearly incorporated into lens crystallins over a 10 day period in the presence of NaCNBH3. This rate of incorporation was 6-7-fold more rapid than that obtained with [14C]glucose under the same conditions. SDS-PAGE showed a linear incorporation into all the crystallin subunits. [1-14C]Ascorbic acid-label led alpha-crystallin was separated into its component A and B subunits, and each was digested with chymotrypsin. HPLC peptide analysis showed a differential labelling of the various lysine residues. Analysis of the peptides by mass spectrometry allowed the identification of the sites and the extent of modification. These values ranged from 6% for Lys-78 to 36% for Lys-11 in the A subunit and from 5% for Lys-82 to an average of 38% for the peptide containing Lys-166, Lys-174 and Lys-175 in the B subunit. Amino acid analysis demonstrated a single modification reaction producing N epsilon-(carboxymethyl)lysine. This agreed with the mass increase of 58 observed for each modified peptide.
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Affiliation(s)
- B J Ortwerth
- Mason Institute of Ophthalmology, University of Missouri, Columbia 65212
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Swamy MS, Abraham A, Abraham EC. Glycation of human lens proteins: preferential glycation of alpha A subunits. Exp Eye Res 1992; 54:337-45. [PMID: 1521566 DOI: 10.1016/0014-4835(92)90046-u] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Glycation of crystallins and high molecular weight (HMW) aggregates was followed during aging (16-85 years) and in diabetes (44 and 70 years old). Lens soluble and insoluble fractions were reduced with [3H]NaBH4 and separated by molecular sieve HPLC. The protein content in each HPLC peak was measured by the Lowry method. The tritium incorporation, expressed as cpm mg-1 protein, was taken as a measure of early glycation and specific non-tryptophan fluorescence (Ex: 370 nm; Em: 440 nm), expressed as relative fluorescence U mg-1 protein, was taken as a measure of advanced glycation. The youngest lenses analysed were 16 and 17 years old and these provided the baseline values. The results showed that during aging there was about a three-fold increase in tritium incorporation and fluorescence of alpha-crystallin, while the increases in beta and gamma were only two-fold from the levels seen in 16- and 17-year-old lenses. On the other hand, both the soluble and insoluble HMW aggregate fractions showed up to five-fold increase in tritium incorporation during aging. The fluorescence was about two-fold higher in the insoluble HMW aggregates as compared to the soluble HMW aggregates in 16- and 17-year-old lenses and both showed an increase of about three-fold during aging. Diabetes resulted in an approximately 10-50% increase in tritium incorporation and non-tryptophan fluorescence of various crystallins and HMW aggregates.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M S Swamy
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100
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19
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Abstract
To investigate the possible role of glycation in the onset of diabetic cataract we used calf lens crystallins as a model. After incubation with reducing sugars, the proteins were investigated by high-pressure gel permeation chromatography, SDS-PAGE and analytical ultracentrifugation. Glucose-6-phosphate incubation resulted in an increase in mean molecular weight of all crystallin fractions and the occurrence of high-molecular weight material, partly formed by disulphide bonds. The glycated crystallins showed a decrease of tryptophan fluorescence and an increase of a specific non-tryptophan fluorescence. This fluorescence was, however, not exclusively associated with the high molecular weight protein, but was present in all protein fractions.
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Affiliation(s)
- M A van Boekel
- Department of Biochemistry, University of Nijmegen, The Netherlands
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20
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Slight SH, Feather MS, Ortwerth BJ. Glycation of lens proteins by the oxidation products of ascorbic acid. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1038:367-74. [PMID: 2340296 DOI: 10.1016/0167-4838(90)90250-j] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Bovine lens water-soluble proteins were incubated with [I-14C]ascorbic acid (ASA) for 6 days, and the incorporation into protein was measured at daily intervals. Aliquots were also withdrawn to determine the distribution of label among the various ASA oxidation products. A linear incorporation into protein was observed in the presence of NaCNBH3, however, little or no incorporation was seen in its absence. TLC analysis showed a complete loss of ASA by day 3, whereas both dehydroascorbate (DHA) and diketogulonic acid (DKG) remained constant for 6 days, consistent with the linear incorporation into protein. The amino acid composition of the proteins glycated in the presence of NaCNBH3 was identical to controls except for a 70% reduction in lysine residues and a corresponding increase in an unknown product which eluted slightly earlier than methionine. In the absence of NaCNBH3 lysine decreased linearly to 20% with an additional decrease in arginine and histidine at later times concurrent with protein crosslinking. DHA and DKG were prepared and incubated directly with lens proteins for an 8 day period. Both compounds glycated lens protein as evidenced by an increased binding to a boronate affinity column. SDS-PAGE showed that both compounds were also capable of causing protein crosslinking. DHA is apparently capable of reacting directly with protein since glycation was observed with the ASA analog, reductic acid, which can be oxidized to dehydroreductic acid, but which cannot be hydrolyzed to an open chain structure. DHA also produced a lysine adduct which was not obtained with DKG, supporting the idea that both species have glycating ability.
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Affiliation(s)
- S H Slight
- Mason Institute of Ophthalmology, University of Missouri, Columbia 65212
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21
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Liang JN, Rossi MT. In vitro non-enzymatic glycation and formation of browning products in the bovine lens alpha-crystallin. Exp Eye Res 1990; 50:367-71. [PMID: 2110908 DOI: 10.1016/0014-4835(90)90137-j] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Calf lens LMW alpha-crystallin was glycated by incubating with various sugars (glucose, glucose-6-P and ribose) for 21 days. All sugars induced disulfide formation, but ribose also produced higher molecular weight cross-linked species. The ribocated protein turned yellow in color and had a strong blue fluorescence (Ex/Em = 370/450 nm) typical for a browning product. The chromophore of the browning product showed a new circular dichroism (CD) band at 320-330 nm. Conformational study indicated that the browning reaction destablized protein and may play a significant role in protein aggregation and insolubilization.
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Affiliation(s)
- J N Liang
- Howe Laboratory of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston 02114
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22
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Yano M, Matsuda S, Bando Y, Shima K. Lens protein glycation and the subsequent degree of opacity in streptozotocin-diabetic rats. Diabetes Res Clin Pract 1989; 7:259-62. [PMID: 2693028 DOI: 10.1016/0168-8227(89)90013-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We measured how much glycated protein there was in rat eye lenses with different degrees of cataract, using an antibody against glucitol-lysine. Streptozotocin-diabetic (STZ) rats were in some cases treated with insulin (STZ + INS); control rats were normal. We graded the cataracts from 0 (transparent) to 3 (entirely opaque). STZ rats had significantly more grade 3 cataracts, and STZ + INS rats more grade 1 cataracts, than other groups. Grade 3 lenses had significantly more glycated protein than those of grade 0 (10.8 +/- 2.7 vs. 1.0 +/- 0.4 nmol/mg protein), grades 1 and 2 being intermediate. Glycosylated hemoglobin levels correlated similarly with severity of cataract. These data are consistent with the greater incidence of cataract among diabetics than among non-diabetics, and suggest that lens protein glycation contributes to the development of cataract.
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Affiliation(s)
- M Yano
- Department of Laboratory Medicine, University of Tokushima, Japan
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23
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Ortwerth BJ, Olesen PR. Glutathione inhibits the glycation and crosslinking of lens proteins by ascorbic acid. Exp Eye Res 1988; 47:737-50. [PMID: 3197774 DOI: 10.1016/0014-4835(88)90041-3] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The incubation of crude extracts of bovine lens with 20 mM ascorbic acid leads to the formation of covalent adducts even in the presence of saturating levels of a metal chelator. When dialysed lens extracts were used both ASA-protein adducts and highly crosslinked lens proteins were observed which are similar to those found in the water insoluble fraction from cataractous lenses. Both adduct formation and protein crosslinking, however, were markedly inhibited if undialysed lens extracts were used or if increasing concentrations of glutathione were added to the incubation mixture. Similar inhibition was seen with cysteine, dithiothreitol and sodium bisulfite, but little effect was observed with the glutathione analog ophthalmic acid or with free radical quenchers. Glutathione was readily oxidized during the incubation and no oxidation of ascorbic acid was observed until all the reduced glutathione was exhausted. No loss of ascorbic acid and no protein crosslinking were observed when oxygen was completely removed from the reaction mixture. These data strongly suggest that the glycating species was an oxidized form of ascorbic acid. Ascorbic acid solutions displayed a rapid oxidation in vitro, which was decreased 80-fold upon the addition of 1 mM chelator and was completely inhibited by both glutathione and chelator. A rapid decrease in the level of dissolved oxygen was seen in the presence of ascorbic acid or ascorbic acid and glutathione, but not with glutathione alone. These data argue that glutathione inhibits glycation by rapidly reducing dehydroascorbic acid back to ascorbic acid, which is not active in protein glycation
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Affiliation(s)
- B J Ortwerth
- Mason Institute of Ophthalmology, University of Missouri, Columbia 65212
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24
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Ortwerth BJ, Olesen PR. Ascorbic acid-induced crosslinking of lens proteins: evidence supporting a Maillard reaction. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 956:10-22. [PMID: 3408736 DOI: 10.1016/0167-4838(88)90292-0] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The incubation of calf lens extracts with 20 mM ascorbic acid under sterile conditions for 8 weeks caused extensive protein crosslinking, which was not observed with either 20 mM sorbitol or 20 mM glucose. While no precipitation was observed, ascorbic acid did induce the formation of high-molecular-weight protein aggregates as determined by Agarose A-5m chromatography. Proteins modified by ascorbic acid bound strongly to a boronate affinity column, however, crosslinked proteins were present mainly in the unbound fraction. These observations suggest that the cis-diol groups of ascorbic acid were present in the primary adduct, but were either lost during the crosslinking reaction or sterically hindered from binding to the column matrix. The amino acid composition of the ascorbic acid-modified proteins was identical to controls except for a 15% decrease in lysine. Amino acid analysis after borohydride reduction, however, showed a 25% decrease in lysine, a 7% decrease in arginine and an additional peak which eluted between phenylalanine and histidine. Extensive browning occurred during the ascorbic acid-modification reaction. This resulted in protein-bound chromophores with a broad absorption spectrum from 300 to 400 nm, and protein-bound fluorophores with excitation/emission maxima of 350/450 nm. A 4 week incubation of dialyzed crude lens extract with [1-14C]ascorbic acid showed increased incorporation for 2 weeks, followed by a decrease over the next 2 weeks as crosslinking was initiated. The addition of cyanoborohydride to the reaction mixture completely inhibited crosslinking and increased [1-14C]ascorbic acid incorporation to a plateau value of 180 nmol per mg protein. Amino acid analysis showed a 50% loss of lysine, and 8% decrease in arginine and the presence of a new peak which eluted slightly earlier than methionine. These data are consistent with the non-enzymatic glycation of lens proteins by either ascorbic acid or an oxidation product of ascorbic acid via a Maillard-type reaction.
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Affiliation(s)
- B J Ortwerth
- Mason Institute of Ophthalmology, University of Missouri, Columbia 65212
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25
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Ortwerth BJ, Feather MS, Olesen PR. The precipitation and cross-linking of lens crystallins by ascorbic acid. Exp Eye Res 1988; 47:155-68. [PMID: 3409983 DOI: 10.1016/0014-4835(88)90032-2] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Bovine lens beta-crystallin was incubated with increasing concentrations of sugars and sugar derivatives for a period of 2 weeks in the dark at 37 degrees C. Marked protein precipitation and a browning reaction was observed with both ascorbic acid (ASA) and dehydroascorbic acid (DHA), but little or no reaction was seen with several other sugars and sugar analogs. Similar incubations were carried out with 20 mM ASA, 20 mM DHA and 20 mM glucose, but with increasing amounts of the individual crystallins. Glucose was capable of precipitating gamma-crystallin in the presence of air, but this reaction was decreased if dithiothreitol and a chelating agent were added prior to incubation. ASA and DHA produced precipitation and browning with gamma- and beta-crystallin, but not with alpha-crystallin or lens soluble proteins. Similar reactivities were observed both in air and under reducing conditions. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of these reaction mixtures showed little or no cross-linking with any of the lens proteins by glucose. ASA and DHA caused detectable dimer formation with gamma-crystallin, but produced the formation of dimers as well as highly polymerized proteins at the top of the gel with all the other crystallins and with lens soluble proteins. A time-course experiment with alpha-crystallin in the presence of air showed no cross-linking with 100 mM glucose over a 6-week period; however, 10 mM ASA caused definite cross-linking at 2 weeks, and at 6 weeks a dark smear of protein was visible throughout the gel. ASA was still capable of inducing cross-linking under low oxygen conditions but the protein smearing was markedly diminished. Further, the cross-linking pattern was similar to that seen in the water-insoluble fraction from older human lenses and cataracts. This reaction may be significant in vivo because cross-linking was observed under low-oxygen conditions with as little as 2 mM ASA, which is the level of ASA normally present in human lenses.
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26
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Ahmed MU, Dunn JA, Walla MD, Thorpe SR, Baynes JW. Oxidative degradation of glucose adducts to protein. Formation of 3-(N epsilon-lysino)-lactic acid from model compounds and glycated proteins. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68379-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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27
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Abstract
The extent of human cataract glycation has been determined by the 5-HMF/TBA method in 236 samples (53 from diabetic patients and 183 from non-diabetic controls). The brownish-yellow coloration typical of the advanced products of the Maillard reaction was measured spectrophotometrically. Glycation of crystallins was three times higher in diabetics than in controls, and was positively correlated with age in the latter group. The two groups did not differ significantly as regards the degree of browning, which was also uncorrelated with the primary products measured by the 5-HMF/TBA method. It is concluded that lens glycation is relatively mild and does not determine the intensity of the characteristic brownish-yellow colour of diabetic and senile cataracts. It is suggested that other coloured compounds produced with age interfere at the relevant wavelengths.
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Affiliation(s)
- P Vidal
- Chair of Physiopathology, Hospital General de Galicia Clinico Universitario, University of Santiago, Santiago de Compostela, Spain
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28
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Yano M, Hashimoto F, Sato M, Ohboshi C, Hirota M, Oshima I, Ohe Y, Shin S, Shima K. Specific radioimmunoassay of glucitol-lysine--application to lens proteins in streptozotocin-diabetic rats. Diabetologia 1988; 31:221-4. [PMID: 3133267 DOI: 10.1007/bf00290588] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
A radioimmunoassay using antibody against glucitol-lysine was developed to quantitate glycated proteins in the lens of diabetic rats. The amount of glycated protein was expressed as molar equivalents of reduced glycated hippuryl lysine (GlcRED-Hip-Lysine). Significant differences (p less than 0.01) were found in the amounts of glycated protein in the lenses of rats with streptozotocin-induced diabetes (3.92 +/- 0.59 nmol/mg protein, n = 5), those with streptozotocin-induced diabetes treated with insulin (2.94 +/- 0.36 nmol/mg protein, n = 4) and normal rats (1.23 +/- 0.22 nmol/mg protein, n = 5). There was a significant correlation between the concentration of glycated protein in the lens and the HbA1c level at the end of the 12 week experiment (r = 0.957, p less than 0.001). These results indicate that glycation of lens protein is parallel with the severity of diabetes in rats.
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Affiliation(s)
- M Yano
- Department of Laboratory Medicine, Tokushima University School of Medicine, Japan
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29
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Oimomi M, Maeda Y, Hata F, Kitamura Y, Matsumoto S, Baba S, Iga T, Yamamoto M. Glycation of cataractous lens in non-diabetic senile subjects and in diabetic patients. Exp Eye Res 1988; 46:415-20. [PMID: 3127229 DOI: 10.1016/s0014-4835(88)80029-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Early- and advanced-stage products in the Maillard reaction, glycation, were measured in patients with diabetic or senile cataracts. Early-stage products were measured by means of furosine, which is an acid-hydrolysis product derived from fructose-lysine. Advanced-stage products were measured by fluorometry using high-performance liquid chromatography. Furosine levels were high (listed in descending order) in capsule, cortex and nucleus in both diabetic and senile cataracts. The advanced-stage products were also high (listed in descending order) in nucleus, cortex and capsule in both diabetic and senile cataracts. These results suggest that advanced-stage products might accumulate in larger amounts in the nucleus and cortex than in the capsule, resulting in the formation of cataracts. The study also revealed that the Maillard reaction plays an important role in causing not only diabetic cataracts but also senile cataracts.
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Affiliation(s)
- M Oimomi
- Second Department of Internal Medicine, Kobe University School of Medicine, Japan
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30
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Abstract
Nonenzymatic glycosylation takes place in all proteins with a free-reacting lysine or valine in the presence of glucose. The formation of glycosylated plasma albumin, hemoglobin (Hb A1c), and skin collagen provides a diagnostic index of short- to long-term time-concentration of glucose in vivo. A wide range of assay methods are available, with affinity chromatographic, isoelectric focusing, and spectrophotometric methods providing the best accuracy and versatility. Glycosylated hemoglobin assays indicate glucose pressure over the previous 2 to 3 months and are of diagnostic value in general diabetic control, while glycosylated plasma albumin determinations are preferable in acute episodes in the life of a diabetic (e.g., pregnancy, infection, stress, trauma, surgery), since they provide an overview of changing blood glucose values of the previous 2 to 4 weeks. Glycosylated collagen estimations reflect tissue aging and are relevant in healing processes. Glycosylation alters the biologic activity of proteins, and these may relate to the manifold complications concomitant on the lifelong elevation of blood and tissue glucose in the diabetic (C6a). Assays for glycosylated hemoglobin have been routinely performed in clinical chemistry laboratories for a decade, and convenient determination for other nonenzymatically glycosylated proteins is proceeding apace.
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31
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Abstract
Lens crystallins undergo non-enzymatic glycosylation with aging and diabetes mellitus. It is not known, however, whether all crystallins are subject to the same extent of glycosylation. Human diabetic lenses (approximately 80 years of age) were dissected into cortex and nucleus, then fractionated into various crystallins with gel chromatography (Sephacryl S-200, Sephadex G-75 or Bio Gel A-15m). The glycosylated crystallins were then separated from the nonglycosylated crystallins by affinity chromatography on Glyco Gel B boronic acid. The percentage of glycosylated crystallin was about 20-30%, and did not differ much among most crystallins, although gamma-crystallin has significantly less (p less than 0.01) glycosylated protein. The extent of glycosylation in the glycosylated crystallins, however, was found to be greater in the high molecular weight crystallins. The extent of glycosylation in alpha-crystallins is approximately two to four times that observed in beta- or gamma-crystallin. The extent of glycosylation appears to depend not only on the lysine content, which does not vary much among the crystallins, but also on the accessibility of the surface areas where lysine residues are located. This accessibility depends on the protein conformation and appears to correlate with protein unfolding.
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32
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Abstract
Binding of lectins to the water-insoluble fractions from human, monkey and mouse lenses was investigated. Lectins bound to glycoproteins blotted from SDS-polyacrylamide gels onto nitrocellulose paper. Use of multiple lectins showed that glycoproteins with apparent molecular weights of about 120 000 and 90 000 were present in all species. These proteins were found in the urea-insoluble fraction. Multiple lectins also bound to two bands around 67 000 and 63 000 molecular weight in both human and monkey lens fractions as well as a urea-soluble band at about 140 000. A 35 000 MW glycoprotein containing N-acetyl-galactosamine and fucose sugars was present in the capsule-epithelium of monkey lenses but was not detected in cortical or nuclear fractions. Glycoproteins from normal and cataractous mice were identified using this new methodology and compared with previously published work using sodium borohydride labelling of glycoproteins. Because of the numerous glycoproteins that can be detected and the ability to assign sugar residues to individual proteins, the lectin-binding method is a powerful tool to investigate lens glycoproteins.
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