| Abstract: | The apparent specific volumes of 17 amino acids are determinedand compared with their tastes and predicted ranges of tastereported in earlier work. Most amino acids elicit many basictastes although one taste usually predominates. All D-aminoacids tasted (except proline and hydroxy prohne) are sweet andseven of the L-amino acids are sweet. Ten of the 16 L-aminoacids are bitter but two of these are both bitter and sweetin accordance with prediction from their apparent specific volumes.‘Spatial barriers’ account for the exclusion ofthe larger L-amino acids from sweet receptors. However, D-proline,the only reportedly purely bitter D-amino acid, is cyclic andthis explains its borderline position between the sweet andbitter regions, and the sweet-bitter taste of L-proline. Lowmol. wt amino acids, irrespective of whether they are D- orL-enantiomers, are always sweet, providing that their apparentspecific volumes are below 0.66 and that they do not generatesuprathreshold concentrations of protons. The two dicarboxylicamino acids, glutamic and aspartic are sour. Apparent specificvolumes represent the effective size of solutes in water dueto their intrinsic molecular architecture. The values reportedhere are used to interpret steric exclusion of certain enantiomersfrom the taste receptors. These results support the idea thatapparent specific volume is a determinant of taste quality. |
