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Dose-Dependent Effects of L-Arginine on PROP Bitterness Intensity and Latency and Characteristics of the Chemical Interaction between PROP and L-Arginine.

Melis M, Arca M, Aragoni MC, Cabras T, Caltagirone C, Castagnola M, Crnjar R, Messana I, Tepper BJ, Tomassini Barbarossa I - PLoS ONE (2015)

Bottom Line: Here, we show that salivary L-Arg levels are higher in PROP super-tasters compared to medium tasters and non-tasters, and that oral supplementation with free L-Arg enhances PROP bitterness intensity as well as reduces bitterness latency in a dose-dependent manner, particularly in individuals with low salivary levels of both free L-Arg and Ps-1 protein.Results showed that the -NH2 terminal group of the L-ArgH+ side chain interacts with the carbonyl or thiocarbonyl groups of PROP by forming two hydrogen bonds with the resulting charged adduct.Our data suggest that L-Arg could act as a 'carrier' of various bitter molecules in saliva.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Sciences, Section of Physiology, University of Cagliari, Monserrato, CA, Italy.

ABSTRACT
Genetic variation in the ability to taste the bitterness of 6-n-propylthiouracil (PROP) is a complex trait that has been used to predict food preferences and eating habits. PROP tasting is primarily controlled by polymorphisms in the TAS2R38 gene. However, a variety of factors are known to modify the phenotype. Principle among them is the salivary protein Ps-1 belonging to the basic proline-rich protein family (bPRP). Recently, we showed that oral supplementation with Ps-1 as well as its related free amino acids (L-Arg and L-Lys) enhances PROP bitterness perception, especially for PROP non-tasters who have low salivary levels of Ps-1. Here, we show that salivary L-Arg levels are higher in PROP super-tasters compared to medium tasters and non-tasters, and that oral supplementation with free L-Arg enhances PROP bitterness intensity as well as reduces bitterness latency in a dose-dependent manner, particularly in individuals with low salivary levels of both free L-Arg and Ps-1 protein. Supplementation with L-Arg also enhanced the bitterness of caffeine. We also used 1H-NMR spectroscopy and quantum-mechanical calculations carried out by Density Functional Theory (DFT) to characterize the chemical interaction between free L-Arg and the PROP molecule. Results showed that the -NH2 terminal group of the L-ArgH+ side chain interacts with the carbonyl or thiocarbonyl groups of PROP by forming two hydrogen bonds with the resulting charged adduct. The formation of this PROP•ArgH+ hydrogen-bonded adduct could enhance bitterness intensity by increasing the solubility of PROP in saliva and its availability to receptor sites. Our data suggest that L-Arg could act as a 'carrier' of various bitter molecules in saliva.

No MeSH data available.


Related in: MedlinePlus

1H-NMR chemical shift variation supporting the formation of the PROP-L-Arg complex.PROP ring 1H-NMR chemical shift (δ) variation with addition of increasing amounts of L-Arg (A), and 1H-NMR spectra recorded on D2O solutions of PROP (0.005 M) upon addition of L-Arg (0.034 M) in D2O (B). Δ = (/(δ'-δ0)//δ0)•100 represents the absolute value of the difference between the 1H-NMR signal (ppm) of the PROP ring proton in the absence (δ0) and in the presence (δ') of the amino acid at the relevant molar ratio, normalized for δ0 and expressed as a percentage. In B, the peak is the signal attributed to the PROP ring proton.
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pone.0131104.g002: 1H-NMR chemical shift variation supporting the formation of the PROP-L-Arg complex.PROP ring 1H-NMR chemical shift (δ) variation with addition of increasing amounts of L-Arg (A), and 1H-NMR spectra recorded on D2O solutions of PROP (0.005 M) upon addition of L-Arg (0.034 M) in D2O (B). Δ = (/(δ'-δ0)//δ0)•100 represents the absolute value of the difference between the 1H-NMR signal (ppm) of the PROP ring proton in the absence (δ0) and in the presence (δ') of the amino acid at the relevant molar ratio, normalized for δ0 and expressed as a percentage. In B, the peak is the signal attributed to the PROP ring proton.

Mentions: 1H-NMR spectroscopy allowed us to determine the PROP ring proton 1H-NMR chemical shift variation, reported as Δ, upon the addition of increasing amounts of amino-acid up to a L-Arg:PROP molar ratio of 1.625:1 (Fig 2A and 2B). The data showed that increasing concentrations of L-Arg induced increased variations of the PROP proton field-shift and of the corresponding 1H-NMR signal.


Dose-Dependent Effects of L-Arginine on PROP Bitterness Intensity and Latency and Characteristics of the Chemical Interaction between PROP and L-Arginine.

Melis M, Arca M, Aragoni MC, Cabras T, Caltagirone C, Castagnola M, Crnjar R, Messana I, Tepper BJ, Tomassini Barbarossa I - PLoS ONE (2015)

1H-NMR chemical shift variation supporting the formation of the PROP-L-Arg complex.PROP ring 1H-NMR chemical shift (δ) variation with addition of increasing amounts of L-Arg (A), and 1H-NMR spectra recorded on D2O solutions of PROP (0.005 M) upon addition of L-Arg (0.034 M) in D2O (B). Δ = (/(δ'-δ0)//δ0)•100 represents the absolute value of the difference between the 1H-NMR signal (ppm) of the PROP ring proton in the absence (δ0) and in the presence (δ') of the amino acid at the relevant molar ratio, normalized for δ0 and expressed as a percentage. In B, the peak is the signal attributed to the PROP ring proton.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477953&req=5

pone.0131104.g002: 1H-NMR chemical shift variation supporting the formation of the PROP-L-Arg complex.PROP ring 1H-NMR chemical shift (δ) variation with addition of increasing amounts of L-Arg (A), and 1H-NMR spectra recorded on D2O solutions of PROP (0.005 M) upon addition of L-Arg (0.034 M) in D2O (B). Δ = (/(δ'-δ0)//δ0)•100 represents the absolute value of the difference between the 1H-NMR signal (ppm) of the PROP ring proton in the absence (δ0) and in the presence (δ') of the amino acid at the relevant molar ratio, normalized for δ0 and expressed as a percentage. In B, the peak is the signal attributed to the PROP ring proton.
Mentions: 1H-NMR spectroscopy allowed us to determine the PROP ring proton 1H-NMR chemical shift variation, reported as Δ, upon the addition of increasing amounts of amino-acid up to a L-Arg:PROP molar ratio of 1.625:1 (Fig 2A and 2B). The data showed that increasing concentrations of L-Arg induced increased variations of the PROP proton field-shift and of the corresponding 1H-NMR signal.

Bottom Line: Here, we show that salivary L-Arg levels are higher in PROP super-tasters compared to medium tasters and non-tasters, and that oral supplementation with free L-Arg enhances PROP bitterness intensity as well as reduces bitterness latency in a dose-dependent manner, particularly in individuals with low salivary levels of both free L-Arg and Ps-1 protein.Results showed that the -NH2 terminal group of the L-ArgH+ side chain interacts with the carbonyl or thiocarbonyl groups of PROP by forming two hydrogen bonds with the resulting charged adduct.Our data suggest that L-Arg could act as a 'carrier' of various bitter molecules in saliva.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Sciences, Section of Physiology, University of Cagliari, Monserrato, CA, Italy.

ABSTRACT
Genetic variation in the ability to taste the bitterness of 6-n-propylthiouracil (PROP) is a complex trait that has been used to predict food preferences and eating habits. PROP tasting is primarily controlled by polymorphisms in the TAS2R38 gene. However, a variety of factors are known to modify the phenotype. Principle among them is the salivary protein Ps-1 belonging to the basic proline-rich protein family (bPRP). Recently, we showed that oral supplementation with Ps-1 as well as its related free amino acids (L-Arg and L-Lys) enhances PROP bitterness perception, especially for PROP non-tasters who have low salivary levels of Ps-1. Here, we show that salivary L-Arg levels are higher in PROP super-tasters compared to medium tasters and non-tasters, and that oral supplementation with free L-Arg enhances PROP bitterness intensity as well as reduces bitterness latency in a dose-dependent manner, particularly in individuals with low salivary levels of both free L-Arg and Ps-1 protein. Supplementation with L-Arg also enhanced the bitterness of caffeine. We also used 1H-NMR spectroscopy and quantum-mechanical calculations carried out by Density Functional Theory (DFT) to characterize the chemical interaction between free L-Arg and the PROP molecule. Results showed that the -NH2 terminal group of the L-ArgH+ side chain interacts with the carbonyl or thiocarbonyl groups of PROP by forming two hydrogen bonds with the resulting charged adduct. The formation of this PROP•ArgH+ hydrogen-bonded adduct could enhance bitterness intensity by increasing the solubility of PROP in saliva and its availability to receptor sites. Our data suggest that L-Arg could act as a 'carrier' of various bitter molecules in saliva.

No MeSH data available.


Related in: MedlinePlus