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HENRYB , BULL
Vol. 67
The thickness of such a molecule from the present study would be 18.1 k. Bull and Cooperlo from viscosity and diffusion data estimated the thickness of the 0-lactoglobulin molecule to be 20 A. Likewise from the present study we conclude that the area of the top face of the duplex molecule would be 3 X 5800 or 2900 sq. k.
3. It has been found that the area of the gaseous, uncompressed a m of @-lactoglobulinis approximately 1.2 sq. meters per milligram of protein from which it is concluded that there is extensive orientation of the side chain residues in the uncompressed state. 4. The film pressure and the corresponding film area has been determined at the point of miniSummary mum compressibility. At this point the @-lacto1. the force-area curve for P-lactoglobulin has globulin film occupies 0.83 sq. meter per millibeen investigated for films of the protein spread gram of protein. The area per molecule and the on 35% ammonium sulfate solution. A Wilhelmy average area per amino acid residue have been balance has been used to record the film pressures. calculated. 2. The &lactoglobulin film is gaseous at low 5 . A tentative attempt has been made to arrive film pressures. The molecular weight of the a t the molecular dimensions of the native @-lacto0-lactoglobulin in the spread film has been esti- globulin molecule. It is concluded that the data mated to be about 44,000. It is concluded that from spread films of this protein are compatible the &lactoglobulin molecules do not associate or with a duplex structure whose dimensions are redissociate on the surface. ported. (10) Bull and Cooper, A m . Assoc. Adw. Sci. Pub. No. 41, 150 (1943).
[CONTRIBUTION FROM
THE
CHICAGO, ILLINOIS
RECEIVEDMAY27, 1944
DEPARTMENT OF CHEMISTRY, NORTHWESTERN UNIVERSITY MEDICAL SCHOOL]
Mixed Monolayers of Egg Albumin and Lauryl Sulfate’ BY HENRYB. BULL
Bull and Neurath2 were able to show that sul- tein to pure NaLS., For example, in the first of a series of 11 test-tubes were placed 10 cc.of the protein solution and fated alkyl detergents are potent denaturing no NaLS. The second tube contained 9 cc. of the protein agents for proteins. This observation has since solution and 1 cc. of the NaLS solution. The last tube been elaborated on by several w ~ r k e r s . * . ~ Jof~ the ~ ~series ~ contained 10 cc. of the NaLS solution and no The sulfated detergents are notable for l&ek sur- protein solution. These solutions were allowed to remain overnight at room temperature and then spread on 35y0 face activity and it appeared profitable to investi- ammonium sulfate solution and the force-area curves degate the action of the detergents on spread mono- termined. No control of the PH of the detergent protein layers of protein. The protein selected was egg mixtures was attempted. The protein was at its isoelecalbumin and the sulfated detergent was sodium tric point and the solutions of the pure sulfated detergents had a pH of 6.9. The 35% ammonium sulfate solution had lauryl sulfate (abbreviated N a U in what is to an apparent pH of 3.1 as obtained with a glass electrode. follow). Results.-Before the results for the mixed Experimental.-The egg albumin was prepared from films are reported it would be well to describe fresh hen’s eggs by the method of Kekwick and CantxmB It was recrystallized three times and dialyzed against dis- some of the properties of the pure NaLS films. tilled water until sulfate free. The NaLS was of a highly NaLS does not form a stable spread film on pure purified grade supplied by the courtesy of the Fine Chemi- water and indeed it is not until the concentration cals Division of the E. I. du Pont and Co.,Inc. Thirty five per cent. ammonium sulfate solution was used as the of the underlying ammonium sulfate solution is underlying solution and the same spreading technique increased up to about 27% that a stable spread was employed as described in a previous paper.O A film of NaLS can be obtained and even a t this Wilhelmy balance registered the film pressure. concentration of ammonium sulfate the spread A solution containing 0.250 mg. of N U per cc. and another solution containing 0.330 mg. of egg albumin per cc. film goes into solution in the ammonium sulfate were prepared. These two solutions were mixed in a series a t a film pressure of about 7 dynes per cm. At of relative concentrations which extended from pure pro- 35% ammonium sulfate in the underlying solution the spread film of NaLS is stable up to high film (1) Presented a t the Symposium on Surface Active Agents and pressures. It was, therefore, decided to confine their Application to Biological Systems held by the Division of our attention in this study to spread films of Physical Chemistry of the American Chemical Society at Cleveland, Ohio, April 4,1944. NaLS on 35% ammonium sulfate solutions. (2) Bull and Neurath. J . Biol. Chcm., 118, 163 (1937). Figure 1 shows force-area curves of NaLS films (3) Anson, Science, SO, 256 (1939). on such a solution. (4) Miller and Anderson, J . Biol. Chcm., 144, 475 11942). It will be noted in Fig. 1 that the NaLS can ex(5) Shock and Fogelson, Pioc. SOC.Exfitl. 23101. Med., 10, 304 (1Q42). hibit two force-area curves. The occasion f o ~ (0) Neurath and Futnam, J. BioZ. Chcm., 150, 263 (1943). these two curves has not as yet been established. (7) Lundgren, Elam and OConnell, W d . , 14% 183 (1943). The films which give the results indicated by the (8) Kekwick and Cannan, Biochcm. J., SO, 227 (1936). half filled circles reached “equilibrium” surface (9) Bull, Tare JOURNAL., 67, 4 (1946).
Jan., 1945 25
MIXBDMONOLADRS OF EGG ALBUMIN AND LAURYL SULFATE
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