Shogren R L, Jamieson A M, Blackwell J, Jentoft N
J Biol Chem. 1984 Dec 10;259(23):14657-62.
The time dependence of the molecular weight, radius of gyration, and hydrodynamic size distribution for porcine submaxillary mucin (PSM) in solution have been studied using static and dynamic light scattering. The weight average molecular weight (Mw) of PSM in 6 M guanidine HCl, pH 7, is initially 3 X 10(6) and decreases with time in three phases: rapidly from 3-2 X 10(6), less rapidly from 2-0.9 X 10(6), and slowly below 0.9 X 10(6). The rates of decrease are much greater at pH 2. The energy of activation associated with each phase is 20 kcal/mol, which is similar to that reported for peptide bond cleavage at an aspartic acid residue. Addition of mercaptoethanol to PSM in 6 M guanidine HCl leads to a rapid decrease in Mw to 0.9 X 10(6), followed by a very slow further decrease. These results suggest that native PSM consists of subunits (Mw = 0.9 X 10(6] that are linked by disulfide bonds to form dimers (Mw = 2 X 10(6] and then higher aggregates. This cross-linking appears to occur at unglycosylated regions of the protein core, which are believed to be richer in aspartic acid than the rest of the molecule.
运用静态和动态光散射技术，研究了猪下颌下粘蛋白（PSM）在溶液中的分子量、回转半径及流体力学尺寸分布随时间的变化情况。在pH 7的6 M盐酸胍中，PSM的重均分子量（Mw）最初为3×10⁶，并随时间分三个阶段下降：从3×10⁶迅速降至2×10⁶，从2×10⁶较慢地降至0.9×10⁶，低于0.9×10⁶后下降缓慢。在pH 2时下降速率要大得多。与每个阶段相关的活化能为20千卡/摩尔，这与报道的天冬氨酸残基处肽键断裂的活化能相似。在6 M盐酸胍中向PSM添加巯基乙醇会导致Mw迅速降至0.9×10⁶，随后非常缓慢地进一步下降。这些结果表明，天然PSM由亚基（Mw = 0.9×10⁶）组成，这些亚基通过二硫键连接形成二聚体（Mw = 2×10⁶），然后形成更高的聚集体。这种交联似乎发生在蛋白质核心的非糖基化区域，据信该区域的天冬氨酸比分子的其他部分更丰富。
