Basic PRPs

P TFA, Guanidine Only 26% of total identified peptides correspond to salivary peptides One hundred and eighty-two of identified peptides are predominantly derived from acidic and basic PRPs, statherins, and histatins ... 

All salivary PRPs have shown affinity for dietary tannins [43] and are easily precipitated [15, 40]. Basic PRPs seem to be more effective in precipitating tannins when compared to acidic and glycosylated PRPs [96]. 

Some recent evidences have shown that a basic PRP binds condensed tannins much more effectively than a-amylase. In Figure 16.10, it can be seen that the light-scattering intensity caused by aggregation increases with the concentration of procyanidins until a maximum after which the light scattered intensity remains constant even with a further increase in tannin concentration. 

Figure 16.9 Complete amino acid sequence of the salivary basic PRP IB8c, aligned to indicate the recurring motifs.

Previous works have shown that a basic PRP (IB8c) binds to condensed tannins much more effectively than a-amylase (de Freitas and Mateus 2002). This can be explained by the 3D structure of proteins a-amylase is a globular protein, and IB8c is likely to adopt an extended random coil conformation, which would allow the protein to offer more contact sites to interact with tannins. However, a-amylase seems to be more specific and selective than PRPs in the aggregation with samples containing different amounts of procyanidins (Mateus et al. 2004c). 

The astringency sensation is felt differently by different tasters (Gawel et al. 2001) probably due to differences in individuals saliva, namely its protein composition (Lesschaeve and Noble 2005 Horne et al. 2002). Recently, a study concerning the characterization of basic PRPs in thirteen normal adults has demonstrated that the protein IB9 was only detected in nine adults saliva, while IB7 was not detected at all (Messana et al. 2004). The salivary flow rate was also described as a factor that varies between subjects and can affect astringency perception (Lesschaeve... 

A recent study by Ayad et al. [101] indicated a qualitative association between basic PRPs and caries different peptides were found in the parotid saliva of 9 caries-free adults, who were life-long residents of Rochester NY prior to water-fluoridation, compared to those found in 9 subjects of similar age with high caries. The authors suggested that proteolytic processing of parotid salivary proteins differs between such groups. 

FIGURE 6.3 Primary structures of basic PRP segments IB7,4, IB934, and full length IB8c protein prepared by solid-phase synthesis the repeated sequences are underlined. 

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