- Studies on N-terminal glycation of peptides in hypoallergenic infant formulas: Quantification of α-N-(2-furoylmethyl) amino acids
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To obtain information about the extent of the early Maillard reaction between the N-termini of peptides and lactose, α-N-(2-furoylmethyl) amino acids (FMAAs) were quantified together with ε-A/-(2-furoylmethyl)lysine (furosine) in acid hydrolyzates of hypoallergenic infant formulas, conventional infant formulas, and human milk samples using RP-HPLC with UV-detection. FMAAs are formed during acid hydrolysis of peptide-bound N-terminal Amadori products (APs), and furosine is formed from the Amadori products of peptide-bound lysine. Unambiguous identification was achieved by means of LC/MS and UV-spectroscopy using independently prepared reference material. The extent of acid-induced conversion of APs to FMAAs was studied by RP-HPLC with chemiluminescent nitrogen detection (CLND). Depending on the corresponding a-A/-lactulosyl amino acid, between 6.0% and 18.1% of FMAAs were formed during hydrolysis for 23 h at 110 °C in 8 N HCl. From espi;-N-lactulosyllysine, 50% furosine is formed under these conditions. Whereas furosine was detectable in all assayed samples, five different FMAAs, α-FM-Lys, α-FM-Ala, α-FM-Val, α-FM-lle, and α-FM-Leu, were exclusively detected in acid hydrolyzates of hypoallergenic infant formulas in amounts ranging from 35 to 396 μmol/100 g protein. Taking the conversion factors into account, modification of N-terminal amino acids in peptides by reducing carbohydrates was between 0.3% and 8.4%. This has to be considered within the discussion concerning the nutritional quality of peptide-containing foods.
- Penndorf, Ilka,Biedermann, Daniela,Maurer, Sarah V.,Henle, Thomas
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- Detection of advanced glycation end-products (AGEs) during dry-state storage of -lactoglobulin/lactose
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Glycation of whey proteins is primarily affected by temperature, water activity, and pH, and leads to changes of the functional and nutritional properties of the proteins. In the case of prolonged storage of mixtures of lactose and -lactoglobulin as a model for dried dairy products under mild heat treatment (60-70°C) in a restricted water environment (aw 0.64) at pH 7, Nε-(carboxymethyl)lysine (CML) and furosine were formed concomitant with glycation of β-lactoglobulin. Indirect ELISA using polyclonal antibodies against advanced glycation end products (AGEs) was shown to correlate with analyses of CML using HPLC and may be used for quality control of dried dairy products. The glycation changed the solubility properties of the protein by forming polymeric carbohydrate products of β-lactoglobulin and AGEs as characterised by SDS-PAGE.
- Jongberg, Sisse,Rasmussen, Michael,Skibsted, Leif H.,Olsen, Karsten
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- Glucoselysine is derived from fructose and accumulates in the eye lens of diabetic rats
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Prolonged hyperglycemia generates advanced glycation endproducts (AGEs), which are believed to be involved in the pathogenesis of diabetic complications. In the present study, we developed a polyclonal antibody against fructose-modified proteins (Fru-P antibody) and identified its epitope as glucoselysine (GL) by NMR and LC-electrospray ionization (ESI)- quadrupole TOF (QTOF) analyses and evaluated its potential role in diabetes sequelae. Although the molecular weight of GL was identical to that of fructoselysine (FL), GL was distinguishable from FL because GL was resistant to acid hydrolysis, which converted all of the FLs to furosine. We also detected GL in vitro when reduced BSA was incubated with fructose for 1 day. However, when we incubated reduced BSA with glucose, galactose, or mannose for 14 days, we did not detect GL, suggesting that GL is dominantly generated from fructose. LC-ESI-MS/MS experiments with synthesized [13C6]GL indicated that the GL levels in the rat eye lens time-dependently increase after streptozotocininduced diabetes. We observed a 31.3-fold increase in GL 8 weeks after the induction compared with nondiabetic rats, and N∈-(carboxymethyl)lysine and furosine increased by 1.7- and 21.5-fold, respectively, under the same condition. In contrast, sorbitol in the lens levelled off at 2 weeks after diabetes induction. We conclude that GL may be a useful biological marker to monitor and elucidate the mechanism of protein degeneration during progression of diabetes.
- Ohno, Rei-Ichi,Ichimaru, Kenta,Tanaka, Seitaro,Sugawa, Hikari,Katsuta, Nana,Sakake, Shiori,Tominaga, Yu-Ki,Ban, Ikuho,Shirakawa, Jun-Ichi,Yamaguchi, Yoshiki,Ito, Emi,Taniguchi, Naoyuki,Nagai, Ryoji
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p. 17326 - 17338
(2019/11/25)
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