Adsorption on folded and unfolded protein molecules and its biological significance

Abstract

The interaction of the protein molecule with substances of biological interest was studied. An increase of adsorption of dyes was found when the polypeptide chain unfolded. Several different methods were used: direct measurement of adsorption on to collapsed protein monomolecular layers, and on to heat-coagulated protein; and the change in the "indicator error" of serum albumin after heat-denaturation, the error with some indicators even reversing in sign. For the preparation of weighable amount of collapsed monolayers, a simple apparatus called the "inversion tube" was devised. Evidence was presented that, in the amoeba, protein molecules unfold at one end of the cell and refold at the other, and that this results in cytoplasmic streaming, amoeboid movement and osmotic work. This hypothesis was supported by tests on the amoeba?s accumulatory mechanism for dyes, and its behaviour towards injected adenosine triphosphate, and towards anaesthetics. (1) Amoebae streaming in neutral red solution accumulated the dye at the rear end of the cell as would happen if unfolded proteins with adsorbed dye folded up there and shed the dye. (2) Microinjection of adenosine triphosphate caused contraction and liquefaction of the amoebas cortical gel, which thus closely parallels actomyosin. Contraction and liquefaction occurred continuously in the amoeba's tail (which was found to be a relatively permanent part of the cell) suggesting a ready chemical interpretation The anticoagulant heparin when injected prevented the gelling of the amoeba's plasmasol. (3) A wide range or volatile lipophilic substances, includin gmany anaesthetics, reversibly expanded the area of the amoebas plasma membrane so that it lifted outwards from the granular cytoplasm, except at the tail. This reflects the high surface pressure and collapse of the plasma membrane in the tail. The part that the folding and unfolding of proteins may play in osmotic work, amoeboid movement, cell division, cytoplasmic streaming in general, rhythmic sol-gel changes, anaesthesia and the mechanism of response to touch was discussed, and its possible application in other fields was indicated.