六爻快速断卦金口诀:求人帮忙翻译文章

The key residues on the protein surface responsible for

biological activity have not yet been identified with

certainty for any of these proteins [20]. Monellin was

found to be 100000 times sweeter than sucrose on a

molar basis [21], followed by Brazzein and Thaumatin

which are 500 times [13] and 3000 times sweeter then

sucrose [14] respectively (the latter two on a weight basis).

All of these proteins have been isolated from plants that

grow in tropical rainforests. Although most of them share

no sequence homology or structural similarity, Thaumatin

shares extensive homology with certain non-sweet

proteins found in other plants [15].

The potential industrial applications of these proteins are

the low calorie sweetener industry and the cola, snacks,

food and chocolate industries.

Brazzein

Brazzein is the smallest, most heat-stable [13] and pH-stable

member of the set of proteins known to have intrinsic

sweetness. The protein, consisting of 54 amino acid residues,

is reported to be between 500 and 2000 times

sweeter than sucrose [22] and represents an excellent

alternative to available low calorie sweeteners. It was originally

isolated from the fruit of an African plant Pentadiplandra

brazzeana Baillon [23]. Heat and pH stability of the

protein make it an ideal system for investigating the

chemical and structural requirements of a sweet-tasting

protein. Based on the wild-type brazzein, 25 mutants were

produced to identify critical regions important for sweetness.

To assess their sweetness, psychophysical experiments

were carried out with 14 human subjects. First, the

results suggest that residues 29–33 and 39–43, plus residue

36 between these stretches, as well as the C-terminus

are involved in the sweetness [24]. Second, charge plays

an important role in its interaction with the sweet taste

receptor [24].

Thaumatin

The thaumatins are a class of intensely sweet proteins isolated

from the fruit of the tropical plant Thaumatococcus

danielli.