which produced a full initial response failed to prolong the effect, whereas 1.2·10−8M hormone caused irreversible stimulation. It appears that only about 10% of the initially occupied receptors were covalently labelled because the log dose response curve was shifted to ∼ 10x higher concentration after a 200 min wash period: EC50 immediately after photolysis was 6 · 10−10M; after 200 min EC50 increased
通过片段缩合法在均相溶液中合成了对
叠氮苯丙
氨酸13 -α-
香兰素([Pap 13 ]-α-MSH),并在三种不同的测定系统中测定了其
生物学活性。相对于α-MSH的
颜料分散活性为65%,用皮纳蛙(Rana pipiens)或非洲爪蟾(Xenopus laevis) t的
黑色素团测得。用培养的小鼠黑素瘤细胞测定的
酪氨酸酶刺激活性为50%。紫外线。在338 nm处辐照含有≤10 -4 M [Pap 13 ]-α-MSH的溶液(强度:10 -3 W·cm -2)导致光标签在<20分钟内完全光解。在这些条件下,[Pap 13 ]-α-MSH被共价插入MSH受体中,从而在非洲爪蟾黑色素中产生持久的
颜料分散(参见[3])。长时间刺激的程度取决于光解过程中使用的激素浓度。产生完全初始反应的1.8·10 -9 M [Pap 13 ]-α-MSH无法延长作用,而1.2·10 -8 M激素引起不可逆的刺激。似乎