Polyphenols association with proteins

Plant Polyphenols and Their Association with Proteins... 

Complex plant polyphenols readily and reversibly associate with proteins and they can precipitate them from dilute solution. This property is however a direct extrapolation of the characteristics of simple phenols themselves. The structural device represented by the plant polyphenols to a great extent obviates the need for a high molal concentration of phenol and it embodies the added feature that cross-linking between different molecular aggregates may be readily achieved. 

Beer contains a mixture of phenolic compounds, averaging about 150-350 mg/L, out of which about two thirds originate in barley and the remaining in hops [11]. Of these, polyphenols present the greatest interest for beer processing and storage, since they tend to associate with proteins into insoluble complexes, leading to the formation of cold haze in beer. 

Although the bulk of the intracellular polyphenols are soluble in aqueous alcohol, a significant amount remains in the AIR, which could obscure the nature of the phenolics associated with the cell wall polymers. It is probable that tissues rich in intracellular polyphenols such as tea shoots and cider apples, contain a relatively higher proportion of polyphenolics associated with the wall polymers, but the nature of these phenolics cannot be obtained using the alcohol-insoluble residues, unless the preparations are extensively purified. The polyphenols appear to be present, to an appreciable extent, in the vacuoles of some of the palisade cells of tea leaves (Selvendran and King, 1976), and this may be true of other tissues. In view of the recent interest in the association of phenolics with some pectic substances, wall proteins, hemicellulosic polymers, and a-cellulose of primary cell walls (Fry, 1983 Selvendran, 1985), the foregoing comments may be pertinent. 

Notes The different components of seaweed S. kjellanianum were separated using different processes. The second column shows the weight of different components, and the third column shows the weight percentage of different components in the entire sample. The fourth column shows the iodine concentration in the different components, and the fifth column shows the percentage of iodine component in the entire sample. It shows that the iodine is mainly associated with proteins, pigments and polyphenol. 

Tea leaf, in common with all plant leaf matter, contains the full complement of genetic material, enzymes, biochemical intermediates, carbohydrates, protein, lipids, and structural elements normally associated with plant growth and photosynthesis. In addition, tea leaf is distinguished by its remarkable content of methylxathines and polyphenols. These two groups of compounds are predominantly responsible for those unique properties of tea that account for its popularity as a beverage. It must be noted that the chemical composition of tea leaf varies with climatic condi-... 

Vitamins (C and E), polyphenolic compounds, and carotenoids are the main groups of antioxidants present in fruits and vegetables. Vitamins are single molecules, but polyphenols and carotenoids are made up of hundreds of compounds with a wide range of structures and molecular masses. The intake of these antioxidants can lead to sustained reduction of the kind of oxidative damage to lipids, proteins, and DNA that is associated with the development of chronic diseases (Evans and Halliwell 2001). 

Despite the fact that crude APPL s are totally soluble in DMF, an important residue is obtained at the end of the solvent sequence (0 100, THF DMF) indicating that the protein-rich fractions require association with the polyphenolic part for their solubilization in DMF (Table VI). Because each APPL has a different amino acid composition, its solubility distribution is also different, but in both cases, the THF fraction is the most lignin-like, with only 1% nitrogen. This is confirmed by FTIR analysis (Fig. 7). As the fractionation proceeds with increasing solvent polarity, the lignin characteristic bands at 1515, 1460, 1265, 1095, 1035, and 810 cm-1 disappear, while the amide characteristic bands at 3290 and 3080 cm-1 appear. 

Studies of the association of polyphenols with proteins have a long history (27). Loomis (28) has succinctly summarised the conclusions of this earlier work. The principal means whereby proteins and polyphenols are thought to reversibly complex with one another are (i) hydrogen bonding, (ii) ionic interactions and (iii) hydrophobic interactions. Whilst the major thrust in earlier work was to emphasize the part played by intermolecular hydrogen bonding in the complexation, Hoff (29) has drawn attention to the possibility that hydrophobic effects may dominate the association between the two species. 

A smaller percentage of the Phaeophyta (59% of taxa) contain MAAs and concentrations in thalli are relatively low (<300 nmol mg-1 protein). The Phaeophyta also excrete colored compounds with UV-absorbing properties.62 Some of these exudates are polyphenolic substances that are usually associated with alleopathy. However, in Ascophyllum nodosum, thallus concentrations are regulated by UV exposure and small herbivores are not deterred, rather they feed preferentially on irradiated algae.59 Since the Chlorophyta and Phaeophyta successfully inhabit intertidal and shallow subtidal areas, they have apparently evolved very efficient protective and repair mechanisms for dealing with UV exposure, but MAAs are probably not the key to their fitness in high light environments. 

Kuhn, D. J., Bums, A. C., Kazi, A., Dou, Q. P. (2004). Direct inhibition of the ubiquitin-proteasome pathway by ester bond-containing green tea polyphenols is associated with increased expression of sterol regulatory element-binding protein 2 and LDL receptor. Biochim. Biophis. Acta, 1682, 1-10. 

The majority of the nitrogen compounds in beer have molecular weights between 5 and 70 kDa. The protein components of this fraction are of particular importance in brewing, as some of them contribute to foam formation (positive effect) while others, in association with polyphenols, lead to haze formation (undesirable effect) [10]. 

Haze formation is mostly attributed to proteins, polyphenols, and their interactions. It is also possible that there are also other factors that inbuence haze formation in beer, but their effect has not been yet clearly debned [ 15]. The amount of haze formed depends both on the concentration of proteins and polyphenols, and on their ratio. Polyphenols can combine with proteins to form colloidal suspensions that scatter light, which creates the cloudy appearance of beer. Beer polyphenols originate partly from barley and partly from hops. The beer polyphenols most closely associated with haze formation are the proanthocyanidins, which are dimers and trimers of catechin, epicatechin, and gaUocatechin. These have been shown to interact strongly with haze-active proteins [13,15-17] and their concentration in beer was directly related to the rate of haze formation [18]. Ahrenst-Larsen and Erdal [19] have demonstrated that anthocyanogen-free barley produces beer that is extremely resistant to haze formation, without any stabilizing treatment, provided that hops do not contribute polyphenols either. Not all proteins are equally involved in haze formation. It has been shown that haze-active proteins contain signibcant amounts of proline and that proteins that lack proline form little or no haze in the presence of polyphenols [13,15-17]. In beer, the source of the haze-active protein has been shown to be the barley hordein, an alcohol-soluble protein rich in proUne [16]. 

Polyphenolic catechins and theaflavins exist as either monomers or polymers in green and black teas, respectively, and are both well known to be inhibitory and bactericidal against Streptococcus spp. They bind to surface proteins of the bacteria, and induce aggregation and inhibit the enzymatic activity of glucosyl transferase. Both teas inhibit salivary and streptococcal amylase, overall, leading to reduction in plaque. Studies in animals have shown that tea consumption reduces caries, and it has been associated with lower caries levels in humans. ... 

Expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) is known to be elevated at sites of inflammation. Studies have been conducted into the effects of EGCG and TF-3 on the expression of these adhesion molecules induced by interleukin-ip (IL-lp) in cultured human umbilical vein endothelial cells (HUVECs). Both compounds significantly inhibited IL-ip-induced protein expression of VCAM and ICAM in dose-dependent manners and were associated with reduced adhesion of leukocytes to HUVECs. The m-RNA level of VCAM-1 was also inhibited by these tea polyphenolics, as was the NF-KB-dependent transcriptional activity induced by IL-lp. It is concluded that these molecules exhibit anti-inflammatory and anti-invasion properties, probably via a route involving blockage of IkB kinase. 

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