Sweet sensitive protein

Widespread occurrence of the mentioned proteins may, according to some authors, be the cause of polysensitization, i.e., sensitivity to many different products and it may account for some cross-reactions, for instance between latex and celery and bananas (Jgdrychowski 2001), which have been observed in peaches, apricots, plums, and apples a high structural affinity between the proteins of the fruits mentioned and respective sweet com proteins has been documented (Pastorello et al. 2001). 

Wine is one of the most complex and interesting matrices for a number of reasons. It is composed of volatile compounds, some of them responsible for the odor, and nonvolatile compounds which cause taste sensations, such as sweetness (sugars), sourness (organic acids), bitterness (polyphenols), and saltiness (mineral substances Rapp and Mandary, 1986). With a few exceptions, those compounds need to be present in levels of 1%, or even more, to influence taste. Generally, the volatile components can be perceived in much lower concentrations, since our organs are extremely sensitive to certain aroma substances (Rapp et ah, 1986). Carbohydrates (monosaccharides, disaccharides, and polysaccharides), peptides, proteins, vitamins, and mineral substances are among the other wine constituents. 

Interestingly, the human TAS1R2/TAS1R3, but not its mouse counterpart, are sensitive to the sweet proteins monellin, thaumatin, and brazzein, and to the artificial sweeteners neo-tame, cyclamate, and aspartame (9-11). This difference provides a molecular explanation for the previous observation that these compounds are sweet for humans but not attractive to rodents (9). The species difference also applies to the inhibitor lactisole that blocks the sweet taste in humans but not in rats, and only inhibits the response of human TAS1R2/TAS1R3 to sweet stimuli (9). 

Just as in olfaction, a number of clues pointed to the involvement of G proteins and, hence, 7TM receptors in the detection of bitter and sweet tastes. The evidence included the isolation of a specific G protein a subunit termed gustducin, which is expressed primarily in taste buds (Figure 32.13). How could the 7TM receptors be identified The ability to detect some compounds depends on specific genetic loci in both human beings and mice. For instance, the ability to taste the bitter compound 6- -propyl-2-thiouracil (PROP) was mapped to a region on human chromosome 5 by comparing DNA markers of persons who vary in sensitivity to this compound. 

For experimental details of peptide isolation and sequence analysis, the reader is referred to Volume XXV of this series. However, standard procedures for disulfide reduction, thiol blocking, and tryptic hydrolysis have to be slightly modified, owing to the extreme sensitivity of the bound label in the completely denatured protein or isolated peptides at pH values above 7. This also puts a limit on the conditions of ion-exchange chromatography and electrophoresis. With peptides from /3-glu-cosidase As from A. wentii, the following half-lives (at 26°) were observed. pH 7.0, 30 hr pH 8.6, 5.4 hr pH 9.0, 0.6 hr. However, the label is very stable under acidic conditions, e.g., pH 2.0, aqueous acetic acid up to 25%, 70% formic acid. A similar observation was made with p-glucosidases from sweet almonds and sucrase-isomaltase. ... 

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