Pekary A E, Chan S I
Int J Pept Protein Res. 1977;9(2):148-56. doi: 10.1111/j.1399-3011.1977.tb03474.x.
The secondary structure within histone IV and its fragments obtained by cyanogen bromide (CNBr) and cleavage at Met 84 has been examined by circular dichroism and spectophotometric pH titration measurements. These studies have confirmed the existence of stable secondary structure within the C-terminal fragment of histone IV (C-peptide which can be perturbed only by 6M urea at pH greater than 8 or 8 M guanidine-HCL. In contrast, the N-terminal fragment (N-peptide) appears to lack significant secondary structure at low ionic strengths but acquires approximately 15% betasheet conformation and 5% alpha-helix upon aggregation at ionic strengths larger than or equal to 0.4. The rates of nitration of the N- and C-peptides by tetranitromethane (TNM) have also been measured as a function of ionic strengths. Under comparable conditions, the rate constant for nitration of the N-peptide was found to be about six times greater than that for the C-peptide, further evidence in support of the presence of stable secondary structure within the C-terminal region of histone IV. After binding these histone IV fragments to DNA, however, the nitration reaction rate constants for the N- and C-peptide in the bound form are found to be 2% and 27% of the corresponding free peptides. Reconstituted nucleohistone IV is about 10% as reactive to TNM as histone IV at comparable ionic strength.
通过圆二色性和分光光度法pH滴定测量，研究了组蛋白IV及其通过溴化氰（CNBr）和在Met 84处裂解得到的片段的二级结构。这些研究证实了组蛋白IV C末端片段（C肽）中存在稳定的二级结构，该结构仅在pH大于8时被6M尿素或8M盐酸胍干扰。相比之下，N末端片段（N肽）在低离子强度下似乎缺乏明显的二级结构，但在离子强度大于或等于0.4时聚集时会获得约15%的β-折叠构象和5%的α-螺旋。还测量了四硝基甲烷（TNM）对N肽和C肽的硝化速率与离子强度的函数关系。在可比条件下，发现N肽的硝化速率常数约为C肽的六倍，进一步证明了组蛋白IV C末端区域存在稳定的二级结构。然而，将这些组蛋白IV片段与DNA结合后，发现结合形式的N肽和C肽的硝化反应速率常数分别为相应游离肽的2%和27%。在可比离子强度下，重组核组蛋白IV对TNM的反应性约为组蛋白IV的10%。
