The Measurement of Surface Films Formed by Hemocyanin, Tobacco Mosaic Virus, Vaccinia, and Bacterium Gallinarum

The studies of Gorter (1), Hughes and Rideal (2), Neurath (3), and Langmuir (4) have shown that proteins are capable of forming surface films of a thickness and area independent of the diameter of the molecule. Depending on the pH and salt concentration of the solution upon which the protein is spread, the surface area may be more than 5 times greater than that to be expected from a monolayer of contiguous spherical molecules. The thickness of such surface films is correspondingly less than the assumed spherical molecular diameter. The proteins so far examined by Gorter develop their maximum spreading at pH 1, and again at the isoelectric point, 1 rag. covering about 1 sq. meter. The same maximum spread may be induced at any pH by the addition of salts (5). This remarkably constant area has been demonstrated for pepsin, trypsin, ovalbumin, and insulin, all having a molecular weight of about 35,000, as well as for zein (6) having a molecular weight 6 times greater. Recently, Philippi (7) has reported film measurements on some of the high molecular weight respiratory proteins. He has found that one of these, derived from Palinurus vulgaris, spread to the same extent as egg albumin at pH 1, but did not spread on solutions of a higher pH. He points out the fact that at pH 1 the molecule of this protein is broken down into smaller components to which he attributes the spreading. I t should be noted that proteins which form films of 1 sq. meter per rag. at pH 1 and at their isoelectric point develop smaller films of the same thickness at other hydrogen ion concentrations. The area of the film is conditioned by the amount which remains on the surface,