Effect of condensed tannins prepared from several forages on thein vitro precipitation of ribulose-1,5-bisphosphate carboxylase (Rubisco) protein and its digestion by trypsin (EC 2.4.21.4) and chymotrypsin (EC 2.4.21.1)
✍ Scribed by McNabb, Warren C; Peters, Jason S; Foo, L Yeap; Waghorn, Garry C; Jackson, Felicity S
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 443 KB
- Volume
- 77
- Category
- Article
- ISSN
- 0022-5142
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✦ Synopsis
A series of in vitro experiments was undertaken to determine the extent to which Sephadex LH-20 treated extracts from a range of temperate forages precipitated ribulose-1,5-bisphosphate carboxylase (Rubisco) and a †ected the enzymatic hydrolysis of Rubisco protein by trypsin and chymotrypsin at a range of pH values. Rubisco was chosen because it represents the principal dietary protein for ruminants fed fresh forages. Condensed tannins (CT) or proanthocyanidins (PA) are routinely puriÐed by chromatography using Sephadex LH-20 as a matrix. However, these extracts contained non-CT phenolics together with PA so the term "CT extractÏ was preferred to "PAÏ to describe the extracts. The in vitro precipitation of Rubisco provided a means to compare the reactivity of the CT extracts. The amount of CT extract required to precipitate all the Rubisco in 10 lg of total soluble leaf protein from white clover (T rifolium repens) when this protein was incubated with CT extracts of L otus corniculatus, L pedunculatus and sainfoin (Onobrychis viciifolia) was similar, with between 25 and 50 lg of extract required. The CT extract of sulla (Hedysarum coronarium) also precipitated all the Rubisco, however this only occurred with 50 lg of the extract. The CT extract of dock (Rumex obtusifolius) precipitated all the Rubisco when 5 lg of extract or greater was incubated with total soluble leaf protein. However, the di †erences between the reactivity of all these CT extracts at a range of pH values appeared to be small. Condensed tannin extracts of L corniculatus and L pedunculatus partially inhibited the hydrolysis of Rubisco by trypsin and chymotrypsin to a similar extent, but the extent of the inhibition was a †ected by pH. The inhibition was greater at pH 6É0 than 7É0, whilst at pH 8É0, CT extracts had little or no a †ect on trypsin and chymotrypsin. It was concluded that, although the precipitation of Rubisco provided an ideal method for comparing CT extracts, reactivity alone was unlikely to account for the di †erences in nutritive value that occur with forages containing CT.
1998 SCI.