A comparison of chemical methods for the determination of available lysine in various proteins

Couch, J. R.; Thomas, Michelle

doi:10.1021/jf60207a033

Cited by 18 publications

(10 citation statements)

References 19 publications

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“…However, reduction by sodium borohydride would produce the secondary amine from a Schiff's base. The secondary amine is not acid labile, and acid hydrolysis after such reduction, followed by amino acid analysis would only detect free amino acids (Couch and Thomas, 1976). Using this approach, we analyzed several aged samples where substantial browning and amino acid losses had occurred.…”

Section: Rfsults and Discussionmentioning

confidence: 99%

Free Amino Acid Stability in Reducing Sugar Systems

Baxter

1995

Journal of Food Science

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Solutions of Eree amino acids were sterilized in different carbohydrate mixtures, at different pH values, and both browning and free amino acid content monitored at different storage temperatures. Results showed the expected behavior of a Maillard process, (e.g., increasing reaction rate with increases in pH, temperature and reducing sugar content). However, only three (tryptophan, histidine and lysine) of the amino acids tested (nine essential + taurine) were notably affected, even under stringent conditions (5O'C storage, glucose containing solution at pH 7.5). Thus many free amino acids could probably be added to most food matrices without Maillard reactions affecting overall protein quality.

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Section: Rfsults and Discussionmentioning

confidence: 99%

Free Amino Acid Stability in Reducing Sugar Systems

Baxter

1995

Journal of Food Science

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“…The number of free lysine groups in each protein was measured with the method of Fields31 and Couch and Thomas32 with some amendments. Briefly, 1.0 mL of 0.1% (w/v) TNBS in 100 m M NaHCO 3 at pH 8.5 (freshly prepared prior to use) was added to 1.0 mL of 2.5 mg/mL protein solution also in 100 m M NaHCO 3 (pH 8.5) and mixed well.…”

Section: Methodsmentioning

confidence: 99%

Electrostatic interactions play an essential role in the binding of oleic acid with α‐lactalbumin in the HAMLET‐like complex: A study using charge‐specific chemical modifications

et al. 2012

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Human α-lactalbumin made lethal to tumor cells (HAMLET) and its analogs are partially unfolded protein-oleic acid (OA) complexes that exhibit selective tumoricidal activity normally absent in the native protein itself. To understand the nature of the interaction between protein and OA moieties, charge-specific chemical modifications of lysine side chains involving citraconylation, acetylation, and guanidination were employed and the biophysical and biological properties were probed. Upon converting the original positively-charged lysine residues to negatively-charged citraconyl or neutral acetyl groups, the binding of OA to protein was eliminated, as were any cytotoxic activities towards osteosarcoma cells. Retention of the positive charges by converting lysine residues to homoarginine groups (guanidination); however, yielded unchanged binding of OA to protein and identical tumoricidal activity to that displayed by the wild-type α-lactalbumin-oleic acid complex. With the addition of OA, the wild-type and guanidinated α-lactalbumin proteins underwent substantial conformational changes, such as partial unfolding, loss of tertiary structure, but retention of secondary structure. In contrast, no significant conformational changes were observed in the citraconylated and acetylated α-lactalbumins, most likely because of the absence of OA binding. These results suggest that electrostatic interactions between the positively-charged basic groups on α-lactalbumin and the negatively-charged carboxylate groups on OA molecules play an essential role in the binding of OA to α-lactalbumin and that these interactions appear to be as important as hydrophobic interactions.

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“…The literature contains a wide range of terms which purport to refer to the amount of lysine in a protein or protein‐containing food which could be utilized by animals including humans (Rutherfurd and Moughan ). Many workers have determined chemically reactive lysine using chemical tests and described it as total available lysine (Rehman ), chemically available lysine (Desrosiers and others ), chemically reactive lysine (Henle and others ), reactive lysine (Friedman and others ; Vigo and others ; Torbatinejad and others ), available lysine (Couch and Thomas ; Fernandez‐Artigas and others ; Rufián‐Henares and others ), and bioavailable lysine (Erbersdobler and Hupe ). In this review, the term chemically reactive lysine will be used for values obtained by chemical analyses.…”

Section: Analysis Of Chemically Reactive and Bioavailable Lysinementioning

confidence: 99%

Blocked Lysine in Dairy Products: Formation, Occurrence, Analysis, and Nutritional Implications

Mehta

Deeth

2015

Comp Rev Food Sci Food Safe

115

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Lysine residues in milk proteins become "blocked" when they react with reducing sugars, particularly lactose, in the Maillard reaction. The blocked or glycated lysines reduce the biological availability of the lysine to metabolic processes and also hinder hydrolysis of the parent protein by digestive enzymes. Heating and storage of milk and milk products are the major promotants of the Maillard reaction and resulting chemical damage to the proteins. Several methods have been proposed to estimate the extent of this protein damage. Two major compounds, furosine, a product of acid hydrolysis of lactulosyl-lysine, the 1st stable product of the Maillard reaction, and carboxymethyl-lysine are used for assessing the early and advanced stages of the Maillard reaction, respectively. In addition, several methods are used for assessing the bioavailability of lysine in a protein; these include chemical, enzymic, and animal-based methods. This review discusses the Maillard reaction and its significance in milk and dairy products, methods of assessing the extent of the reaction and of the bioavailability of lysine, and the nutritional significance of blocked lysines and associated Maillard reaction products in milk proteins.

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A comparison of chemical methods for the determination of available lysine in various proteins

Cited by 18 publications

References 19 publications

Free Amino Acid Stability in Reducing Sugar Systems

Free Amino Acid Stability in Reducing Sugar Systems

Electrostatic interactions play an essential role in the binding of oleic acid with α‐lactalbumin in the HAMLET‐like complex: A study using charge‐specific chemical modifications

Blocked Lysine in Dairy Products: Formation, Occurrence, Analysis, and Nutritional Implications

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