Ähnlichkeiten zwischen dem Trübungsverhalten nichtionischer Tenside und der Denaturierung von Biopolymeren, sowie der Einfluß von Anionen auf beides / Similarity between the clouding of nonionic surfactants and the denaturation of biopolymers, and the effect of anions on both phenomena

Abstract

The first topic is a study of the similarity between the clouding phenomenon of micellar solutions of nonionic surfactants (NS) and the thermal denaturation of globular proteins and other native biopolymers. It was prompted by the resemblance between micelles of NS and globular proteins, which was reported previously. The reversible precipitation of NS at their cloud point (CP) occurs in a temperature range of ? 1°C. The reversible denaturation/precipitation of biopolymers spans broader temperature ranges because of the complexity of their secondary and tertiary structures. The main topic is a comparison of the effect of anions in salting NS in or out and in denaturing or stabilizing native biopolymers. This extends our study of the analogy between protein denaturation and clouding of NS: While all organic protein denaturants previously studied salted NS in, many electrolytes salt NS out and stabilize native biopolymers. According to their effect on the structure of water, anions either disrupt or enhance the self-association of water molecules via hydrogen bonds. Structure-breaking anions salt in NS, raising their CP, and denature biopolymers, lowering their denaturation or melting temperature (T m ). Water structure-making anions lower the CP of NS and stabilize native biopolymer structures by raising the T m . (The cations Na + , K + , and NH 4 + enhance the structure of water, salt out NS, and stabilize the native structure of biopolymers, but their effects on CP and T m are comparatively small.) The CP moves in the opposite direction to the T m because NS, unlike biopolymers, have an inverse temperature - solubility relation. Linear relationships with excellent correlations (r ? -0.9) were found between the capacity of anions to shift the CP of NS, and their capacity to alter the secondary, tertiary and quaternary structures of biopolymers as illustrated by the following examples: the denaturation/renaturation of BSA in the presence of urea, and of DNA; the rate of formation of collagen folds in gelatin solutions; shifts in the melting point of gelatin gels; reduction of enzymatic activity; changes in the polymerization of globular proteins; dissociation/association between myosin and actin, and between antigens and antibodies; the disruption of mitochondria. These quantitative correlations corroborate the analogy between denaturation of biopolymers and clouding of NS. They also make it possible to estimate the capacity of anions to disrupt or stabilize biopolymer structures from the anions' effect on the CP of NS. While many of the biochemical procedures for assessing denaturation are complex and cumbersome, CP measurements are fast, easy, and reproducible.