Isolation and chemical properties of multiple active principles from miracle fruit

The active principle of miracle fruit which modifies the taste of sour stimuli into a sweet taste was purified by electrofocusing and its chemical propeorties were determined. The electrofocusing resulted in separation of three species of the active proteins (I, II and III) whose isoelectric points were 9.3, 9.0 and 8.0, respectively. Application of three proteins to polyacrylamide gel electrophoresis gave single bands, respectively. All the proteins had the same molecular weight of 40 000–41 000. Essential difference was not found between amino acid compositions of these proteins. N-terminal amino acid residue of the three proteins was determined to be 16% (w/w) for protein I, 20% (w/w) for protein II and 41% (w/w) for protein III. Eight species of carbohydrates (l-fucose, d-mannose, d-galactose, d-glucose, d-xylose, l-arabinose, l-rhamnose and d-glucosamine) were identified by gas chromatography and amino acid analysis as being carbohydrate components of protein II, which was an abundant component, and their relative contents were determined. 1·10⁻⁸ M protein II was sufficient to induce the half-maximal sweet-inducing activity.