Van Houten J L, Cote B L, Zhang J, Baez J, Gagnon M L
Department of Zoology, University of Vermont, Burlington 05405.
J Membr Biol. 1991 Jan;119(1):15-24. doi: 10.1007/BF01868536.
A doublet of proteins (approximately 48,000 Mr) from the Paramecium cell body membrane fits several criteria for the external cAMP chemoreceptor. These criteria include: (i) selective elution from a cAMP affinity column, matching a specificity that could be predicted from the behavioral response and whole-cell binding; (ii) binding to wheat germ agglutinin indicating the presence of carbohydrate moieties indicating surface exposure; and (iii) selective inhibition of the intact cells' chemoresponse to cAMP by antibodies against the doublet. Additional evidence for the existence of a receptor, in general, comes from selective elimination of the cAMP chemoresponse by photoaffinity labeling of while cells with 8-N3-cAMP. The doublet proteins are not identical to the regulatory subunit of a cAMP-dependent protein kinase from Paramecium, the Dictyostelium cAMP chemoreceptor, or the 42-45 kDa range proteins related to the large surface glycoprotein in Paramecium. The doublet proteins are not readily separable and, as in Dictyostelium, may represent two different covalent modification states of the same protein. Amino acid analysis indicates that the proteins are similar, but does not distinguish between the possibilities of proteolysis and covalent modification. Once cloned, this doublet may prove to be only the fifth external, eukaryotic chemoreceptor to be identified.
来自草履虫细胞体膜的一组双重蛋白质（约48,000 Mr）符合外部cAMP化学感受器的多项标准。这些标准包括：（i）从cAMP亲和柱上选择性洗脱，与从行为反应和全细胞结合中预测的特异性相匹配；（ii）与麦胚凝集素结合，表明存在碳水化合物部分，提示表面暴露；（iii）针对该双重蛋白质的抗体对完整细胞对cAMP的化学反应具有选择性抑制作用。一般来说，关于受体存在的额外证据来自用8-N3-cAMP对完整细胞进行光亲和标记后对cAMP化学反应的选择性消除。该双重蛋白质与草履虫的cAMP依赖性蛋白激酶的调节亚基、盘基网柄菌的cAMP化学感受器或与草履虫中大型表面糖蛋白相关的42 - 45 kDa范围的蛋白质不同。该双重蛋白质不易分离，并且如同在盘基网柄菌中一样，可能代表同一蛋白质的两种不同共价修饰状态。氨基酸分析表明这些蛋白质相似，但无法区分蛋白水解和共价修饰的可能性。一旦克隆成功，这组双重蛋白质可能会被证明是已鉴定的第五种外部真核生物化学感受器。
