Hvidt S, Lehrer S S
Department of Chemistry, Roskilde University, Denmark.
Biophys Chem. 1992 Nov;45(1):51-9. doi: 10.1016/0301-4622(92)87023-c.
The thermally induced unfolding of the alpha-helix of Rana esculenta alpha alpha, alpha beta and beta beta tropomyosin and two tryptic fragments approximately corresponding to the N- and C-terminal halves of alpha beta have been investigated by use of optical rotation, circular dichroism and UV difference spectroscopy. Reversible unfolding transitions of alpha alpha and beta beta occur around 49 degrees C and 32 degrees C, respectively. The helix unfolding of alpha beta shows two major transitions at 36 degrees C and 48 degrees C, with only the latter being reversible. The major unfolding transitions of each of the N- and C-terminal alpha beta peptides roughly correspond to the low and high temperature transitions of intact alpha beta, respectively. This suggests that the unfolding of alpha beta could be due to unfolding of two independent domains in alpha beta. UV difference data, crosslinking and chromatography results show, however, that the unfolding of alpha beta at 36 degrees C is due to chain exchange with the formation of alpha alpha homodimers and largely unfolded beta monomers, and that the transition at 48 degrees C is due to unfolding of alpha alpha dimers.
利用旋光、圆二色性和紫外差光谱法研究了食用蛙αα、αβ和ββ原肌球蛋白的α-螺旋热诱导展开以及两个分别大致对应于αβ N端和C端一半的胰蛋白酶片段。αα和ββ的可逆展开转变分别发生在约49℃和32℃。αβ的螺旋展开在36℃和48℃显示出两个主要转变，只有后者是可逆的。N端和C端αβ肽各自的主要展开转变大致分别对应于完整αβ的低温和高温转变。这表明αβ的展开可能是由于αβ中两个独立结构域的展开。然而，紫外差光谱数据、交联和色谱结果表明，αβ在36℃的展开是由于链交换形成αα同二聚体和大量展开的β单体，而48℃的转变是由于αα二聚体的展开。
