问：组成抗原表位的一些氨基酸是疏水还是亲水的？为什么？还有组成信号肽的氨基酸是疏水还是亲水的？为什么？请高手赐教，感激不尽！

答：信号肽序列在10-40个氨基酸残基范围，其中部有一段长度为10-15个氨基酸殘基的由高度疏水性的氨基酸组成的肽链。一般蛋白质是很难通过脂膜的，但信号肽可引导它通过膜到达特定的部位。

组成抗原表位的氨基酸则不一定是疏水的。看看这段话就清楚了：

The antigenicity profile methods are based on the assumption that specific physicochemical profiles of sequences side chains, invariably corresponds with immunodominant regions of protein. Different groups have used different scales to define the antigenic potential profile along the protein sequence e.g. inverted hydrophobicity scales, scales of turns, Flexibility scales etc. The algorithms are mainly available in the form of commercial (PeptideStructure and PepPlot of GCG, Protean module of DNAstar) or freeware packages (EMBOSS, ProWin) etc.

Good luck!