Lum C K, Henkin R I
Biochim Biophys Acta. 1976 Feb 24;421(2):380-94. doi: 10.1016/0304-4165(76)90304-4.
Binding of various sugars was compared in purified subfractions of taste buds isolated from bovine circumvallate papillae and of non-taste bud-bearing epithelium isolated from tissue surrounding these papillae. Binding of 14C-labeled sugars was greater in purified subfractions obtained from taste bud than from non-taste bud-bearing tissue and was, in general, greater in those taste bud subfractions in which a greater membrane purification was achieved. Binding specificity of the 14C-labeled sugars sucrose, fructose, glucose and of 14C-labeled cyclamate and saccharine was measured by competition of each 14C-labeled sugar or synthetic sweetener with its unlabeled homologous sugar in P4(B) taste bud subfractions; this binding, as shown for sucrose, was reversible and temperature dependent. Essentially no competition of the 14C-lageled sugars sucrose, fructose, glucose or 14C-labeled cyclamate and saccharine by their respective unlabeled homologues occurred in epithelial tissue P4(B) subfractions; this binding was not reversible. Binding specificity was further observed by the competition of 14C-labeled sucrose, fructose and glucose with each unlabeled sugar for binding sites on P4(B) taste bud subfractions; unlabeled sucrose was more effective in competing with each 14C-labeled surgar than was unlabeled fructose or glucose. The relatively non-sweet sugar lactose did not compete with 14C-labeled lactose in P4(B) subfractions from either taste bud or non-taste bud-bearing epithelial tissue. Binding of 14C-labeled sucrose in purified P4(B) bud subfractions was inhibited by increased concentrations of unlabeled sucrose, phospholipase C, neuraminidase, EDTA, NaCl and urea. Dissociation constants for sugar or synthetic sweetener binding were low (approx. 10(-3) M) but in a rank order (sucrose greater than fructose greater than glucose greater than saccharine) consistent with preference and electrophysiological responses in cow. The cow is behaviorally indifferent to saccharine and lactose consistent with the data obtained in the present study.
比较了从牛轮廓乳头分离出的味蕾纯化亚组分以及从这些乳头周围组织分离出的无味蕾上皮中各种糖类的结合情况。从味蕾获得的纯化亚组分中，14C标记糖类的结合量比从无味蕾组织中的更多，并且一般来说，膜纯化程度更高的味蕾亚组分中结合量更大。通过在P4(B)味蕾亚组分中，每种14C标记糖类或合成甜味剂与其未标记的同源糖类竞争，测定了14C标记糖类蔗糖、果糖、葡萄糖以及14C标记甜蜜素和糖精的结合特异性；如蔗糖所示，这种结合是可逆的且依赖温度。在P4(B)上皮组织亚组分中，14C标记糖类蔗糖、果糖、葡萄糖或14C标记甜蜜素和糖精基本上不会被它们各自未标记的同源物竞争；这种结合是不可逆的。通过14C标记蔗糖、果糖和葡萄糖与每种未标记糖类竞争P4(B)味蕾亚组分上的结合位点，进一步观察到结合特异性；未标记的蔗糖比未标记的果糖或葡萄糖在与每种14C标记糖类竞争时更有效。相对不甜的乳糖在来自味蕾或无味蕾上皮组织的P4(B)亚组分中不会与14C标记的乳糖竞争。纯化的P4(B)味蕾亚组分中14C标记蔗糖的结合会受到未标记蔗糖、磷脂酶C、神经氨酸酶、EDTA、NaCl和尿素浓度增加的抑制。糖类或合成甜味剂结合的解离常数较低（约10(-3) M），但呈蔗糖＞果糖＞葡萄糖＞糖精的顺序，这与牛的偏好和电生理反应一致。牛在行为上对糖精和乳糖无偏好，这与本研究获得的数据一致。
