Biochemical studies of taste sensation. IX. Enhancement of L-[3H]glutamate binding to bovine taste papillae by 5'-ribonucleotides.
The interaction of the taste substance monosodium L-glutamate with taste receptors has been investigated. Binding of L-[3H]glutamate was measured to preparations of bovine circumvallate (taste) papillae (type I preparation) and to control tongue epithelial preparations (type II preparation) devoid of taste receptors. Binding is operationally defined using a membrane filtration assay. Substantially greater binding occurred to the type I preparation than to the type II preparation, and the binding to the type I preparation showed evidence of saturation. The apparent Kd of L-glutamate was estimated to be in the range of 20--30 mM. The unique taste effect of L-glutamate was considered to depend importantly on its demonstrated synergism in combination with certain 5'-ribonucleotides. A several-fold enhancement of binding of L-[3H]glutamate occurred in the presence of certain 5'-ribonucleotides. 5'-GMP, 5'-IMP and 5'-UMP each increased the binding of L-[3H]glutamate, while 5'-XMP, 5'-AMP and 5'-CMP did not. None of these nucleotides affected the lower level of binding to the type II preparation. Neither the free bases, adenine and guanine, their nucleosides nor their di- or triphosphonucleotides were effective in increasing L-[3H]glutamate binding to the type I preparation. The nucleotide specificity of the glutamate binding enhancement therefore shows a marked similarity with the nucleotide specificity in evoking the synergistic taste effect in humans.
D000818:Animals; D002417:Cattle; D005971:Glutamates / Q000378:metabolism*; D006157:Guanosine Monophosphate / Q000378:metabolism; D007291:Inosine Monophosphate / Q000378:metabolism; D012265:Ribonucleotides / Q000378:metabolism*; D012970:Sodium Glutamate / Q000378:metabolism; D013649:Taste / Q000502:physiology*; D013650:Taste Buds / Q000378:metabolism*; D014059:Tongue / Q000378:metabolism; D014542:Uridine Monophosphate / Q000378:metabolism
D005971:Glutamates; D012265:Ribonucleotides; D007291:Inosine Monophosphate; D006157:Guanosine Monophosphate; D014542:Uridine Monophosphate; D012970:Sodium Glutamate