Thaumatin

Literature References: Sweet-tasting basic protein extracted from the fruit of the tropical plant, Thaumatococcus danielli Benth., Marantaceae, found in Western Africa from Sierra Leone to Zaire, in Sudan and Uganda. Composed of five different forms, thaumatins I, II, III, b and c; thaumatins I and II predominate. All are nearly 100,000 times sweeter than sucrose and have molecular weights of about 22,000. Isoln and characterization: H. van der Wel, K. Loeve, Eur. J. Biochem. 31, 221 (1972). Extraction process: J. Higgenbotham, US 4011206 (1976 to Tate and Lyle Ltd.). Electrophysical study of effects on taste receptors: Brouwer et al., Acta Physiol. Scand. 89, 550 (1973). Spectrometric investigation: O. Korver et al., Eur. J. Biochem. 35, 554 (1973). Studies on the primary structure of thaumatin I: R. B. Iyengar et al., ibid. 96, 193 (1979). Thaumatins I and II consist of almost identical sequences of 207 amino acids. Thaumatin I crystallizes in two different forms: H. van der Wel et al., FEBS Lett. 56, 316 (1975). The crystal structure shows two distinct regions with the amino acids either in sheets or in complex loops. Crystal structure: A. M. de Vos et al., Proc. Natl. Acad. Sci. USA 82, 1406 (1985). Cloning and expression in E. coli of the structural gene of thaumatin II: L. Edens et al., Gene 18, 1 (1982); C. T. Verrips, EP 54330; EP 54331 (both 1982 to Unilever). Cloning of the natural gene: A. M. Ledeboer et al., Gene 30, 23 (1984). Reviews: R. Cagan, Science 181, 32 (1973); H. van der Wel, Chem. Ind. (London) 1983, 19.

Properties: Intensely sweet taste, licorice aftertaste. Strongly cationic, isoelectric pt greater than or equal to 11.7. uv max: 278 nm (pH 5.6); 283, 290 nm (pH 13.0). About 750-1600 times sweeter than sucrose on a wt basis; 30,000-100,000 times on a molar basis. Threshold values are near 10-4%. The proteins lose sweetness on heating, on splitting of disulfide bridges and also at pH < 2.5 which points to the importance of the tertiary structure for the sweetness.