Padmanabhan S, Baldwin R L
Department of Biochemistry, Stanford University Medical School, CA 94305.
J Mol Biol. 1991 May 20;219(2):135-7. doi: 10.1016/0022-2836(91)90553-i.
For comparison with earlier data on naturally occurring non-polar amino acids (Ala, Leu, Phe, Val, Ile), the comparative helix-forming tendencies have been measured for non-polar amino acid residues that have unbranched side-chains, with an ethyl, propyl or butyl group, and also for methionine. The substitutions are made in a 17-residue alanine-based peptide. The results show that straight-chain non-polar amino acids have high helix-forming tendencies compared to beta-branched non-polar amino acids. Restriction of side-chain conformations in the helix, with a corresponding reduction in conformational entropy, is the likely explanation. There is a small increase in helix-forming tendency as the side-chain increases in length from ethyl to butyl, which suggests that a helix-stabilizing hydrophobic interaction is being detected.
为了与早期关于天然存在的非极性氨基酸（丙氨酸、亮氨酸、苯丙氨酸、缬氨酸、异亮氨酸）的数据进行比较，已对具有直链侧链（带有乙基、丙基或丁基）的非极性氨基酸残基以及甲硫氨酸的相对螺旋形成倾向进行了测量。这些取代是在一个基于17个残基的丙氨酸肽中进行的。结果表明，与β-支链非极性氨基酸相比，直链非极性氨基酸具有较高的螺旋形成倾向。螺旋中侧链构象的限制以及相应的构象熵降低可能是其原因。随着侧链长度从乙基增加到丁基，螺旋形成倾向略有增加，这表明检测到了一种稳定螺旋的疏水相互作用。
