Morris J A, Cagan R H
Proc Soc Exp Biol Med. 1975 Nov;150(2):265-70. doi: 10.3181/00379727-150-39017.
Effects of the denaturants urea and guanidine-HCl on the sweet-tasting protein monellin have been studied. The pH at which monellin is initially treated with denaturant is an important factor in retention of sweetness, but the pH maintained during subsequent removal of denaturant by dialysis has no effect on activity. Recovery of sweetness of denaturant-treated monellin is favored when denaturation occurs at acid pH. Monellin treated with either 6 M guanidine-HCl or 8 M urea at acid pH retains all of its sweetness following removal of denaturant, but urea treatment at neutral pH leads to some irreversible loss of sweetness. Monellin precipitates from solution under some conditions during removal of denaturant by dialysis, and the precipitated protein is no longer sweet. Precipitation is least under acid conditions. Aggregated protein was demonstrated by gel filtration chromatography. The single sulfhydryl group of monellin was not demonstrable in the precipitated protein, having apparently become oxidized during denaturation and formation of the aggregated protein. The data support the hypothesis that the tertiary structure is important in the ability of monellin to elicit a sweet sensation.
已对变性剂尿素和盐酸胍对甜味蛋白莫内林的影响进行了研究。莫内林最初用变性剂处理时的pH值是保留甜味的一个重要因素，但随后通过透析去除变性剂过程中维持的pH值对活性没有影响。当在酸性pH值下发生变性时，变性剂处理过的莫内林甜味的恢复更有利。在酸性pH值下用6M盐酸胍或8M尿素处理的莫内林在去除变性剂后保留了其所有甜味，但在中性pH值下用尿素处理会导致一些不可逆的甜味损失。在通过透析去除变性剂的过程中，莫内林在某些条件下会从溶液中沉淀出来，沉淀的蛋白质不再有甜味。在酸性条件下沉淀最少。通过凝胶过滤色谱法证明了蛋白质的聚集。莫内林的单个巯基在沉淀的蛋白质中无法检测到，显然在变性和聚集蛋白形成过程中已被氧化。这些数据支持了三级结构对莫内林产生甜味感觉的能力很重要这一假设。
