T H E INTERACTION BETWEEN PROTEINS AND FATTY ACIDS ON THE SURFACE OF AQUEOUS SOLUTIONS’r2 HANS NEURATHa
Department of Chemistry, Cornell University, Ithaca, New York Received June 88, 1987
The problem of the interaction between proteins and lyophobic substances seems to be of interest in regard to the structure of proteins, since it bears upon the function of the lyophilic and lyophobic groups as well as on the structure of certain biological systems which consist mainly of proteins and such lyophobic materials as fats and lipids. The membranes of the living cells are examples of such systems, and their structure and function depend not only on the chemical composition but to a large extent also on the orientation of the individual compounds on the surface. A relatively easy way of studying such system is provided by the method of spreading in surface films, inasmuch as proteins in the cell membranes as well as on the surface of aqueous solutions are probably present in the surface-denatured state (6). Such studies have been carried out recently by Hughes ( 7 ) and by Schulman and Hughes (10). Their investigations differ essentially, however, from those described in this paper, ifi that they studied the phenomenon of “film penetration” by injecting the protein underneath a film of fatty acids and similar materials, whereas in these experiments proteins and the lyophobic material were spread simultaneously in order to ascertain complete spreading. In order to deal with relatively simple and well-defined systems, instead of fats and lipids, fatty acids such as stearic acid, palmitic acid, or myristic acid were chosen for these studies. Of these acids only myristic acid gave satisfactory results under the conditions of spreading used. The experiments reported below are to be regarded as preliminary; publication at the present stage seemed desirable, however, as many data have been accumulated and a partial analysis of the problem accomplished. 1 Presented a t the Fourteenth Colloid Symposium, held a t Minneapolis, Minnesota, June 10-12, 1937. e The experimental part of this paper was carried out in 1934-35 a t the University College, London, England. The author is greatly indebted to Professor F. G. Donnan, F.R.S., for his hospitality and for his interest in these investigations. George Fisher Baker Research Fellow. 39
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HAXS NEURATH EXPERIhIESTAL
A . Preparation of solutaons O.ialbuniii solutions were prepared in exactly the same manner a$ described in the previous paper (S), i.e., by separating the yolk of fresh hens' eggs froin the white, diluting the latter with distilled mater, and filtering off the precipitated globulins. The filtrate was electrodialyzed in Pauli's apparatus (9) for several days, the voltage being gradually iritrrasrd from 5 t o 220 volts After seven days the conductivity had rear}.( d its niiriimal d u e of 81 OW5 mhos with 2 per cent protein solution (pH 4 80) Ailiieouq solutions of fatty acid were prepared by dissolving the acid firb+ iii a minimal volume of 96 per cent ethyl alcohol and adding to this -oh; on dilute potassium hydroxide until a water-clear solution resulted. This soap solution was spread on NIlO hydrochloric acid, thus forming a film of the free fatty acid on the surface When using palmitic acid it was ,
