Collagen is composed of fibrils that are formed by self-assembly of smaller units, monomers which are triple-helical polypeptide. However, the mechanism of fibril formation at the level of individual molecules has remained to be clarified. We found that the fluorescence of thioflavin T, which has been widely used as a specific dye for amyloid fibrils, also increased by binding with fibrils of atelocollagen prepared from yellowfin tuna skin. There was a linear correlation between the fluorescence increase and the amount of atelocollagen within a collagen concentration range of 0-0.15 mg/ml at pH 6.5 with 50 microM thioflavin T. In contrast, neither actinidain-processed collagen that keeps monomeric nature nor heat-denatured collagen could cause the fluorescence increase of thioflavin T at all. The relationship between the fluorescence increase and thioflavin T concentration was fit to a theoretical binary binding curve. An apparent dissociation constant, K(d), and a maximal fluorescence increase, DeltaF(max), were calculated at various pHs. The values of K(d) and DeltaF(max) were dependent on pH (K(d) was 9.4 microM at pH 6.5). The present finding demonstrates that thioflavin T specifically binds to collagen fibrils and may be used as a sensitive tool for the study of collagen structure.

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Food extracts from spices and teas were examined for the taste altering ability on sweet, umami and bitter tastes by using the taste sensation test. The idea arose based upon the findings that 1) some food extracts from spices and teas act as salt taste enhancers and 2) the enhancing effect is directly proportional to glutamate decarboxylase 67 (GAD67) activity in vitro. Our results indicated that those extracts significantly activated or inhibited GAD67 enzyme activity were able to alter sweet, umami, and bitter tastes. However, there were no relationships between the taste potency of each of the examined extracts and the GAD67 relative activity ratio. While it is unlikely that the extracts have directly activated GAD67 activity and enhanced sweet, umami or bitter tastes, the results do not exclude the idea that GABA may participate in the taste cell-to-cell communications.

No abstract