The effects of protein denaturation vary according to the kind of protein and the nature of the denaturing agent (4,6,8,11,13). Reversibility of heat denaturation appears to be limited to serum albumin. No reversibility has been detected so far in other proteins submitted to heat denaturation nor in any protein submitted to ultraviolet light coagulation (5, 10). Further differences in the changes brought about in proteins by heat and by light of short wave length become manifest in rotatory dispersion ( 9) and in optical absorption (17). Since especially the latter results seem to point to structural differences between heat-denatured and ultraviolet-light-denatured serum albumin, comparative x-ray studies seemed warranted. This method of investigation has the advantage that problems of solubility and dispersion do not interfere with the results. APPARATUSThe x-ray apparatus used in these studies has been described previously (15). The tube operates at 35 kilovolts peak with an average current of 15 milliamperes and is equipped with a copper target, aluminumfoil windows (0.013 mm.), and lead diaphragms (1 mm. in diameter and 47 mm. in effective length). The specimen is tightly packed into a hole drilled through a glass slide of 1.32 mm. thickness and is 88 mm. from the focal spot and 37.7 mm. from the film. An exposure time of 1 hr. was used in most cases. The moisture content of the cameras can be varied. The photometric evaluation of the x-ray diffraction patterns was done with the help of a photoelectric microdensitometer described by . By using a special technique for an exact determination of the center of the diffraction pattern, the relative light transmissions 1 Presented March 14, 1940 at the Meeting of the American Society of Biological Chemists, held in New Orleans, Louisiana.! This work was aided by a grant to one of us (M. Sp.-A) from the National Research Council Committee on Radiation.
ALTHOUGH extensive investigations [Remesow, 1930] have been made recently on the physico-chemical behaviour of some lipoid sols, explanations are still lacking of some problems interesting to the biologist. Of these problems, the specific therapeutic effect of bromides and the relation of lipoids to proteins have been chosen for a physico-chemical investigation. In a previous paper [Spiegel-Adolf, 1932], an in vitro analogy with the specific effect of bromides on the substance of the central nervous system was demonstrated. While the Hofmeister series of anions gives no clue in this direction, it could be shown that bromides have a stronger depressing effect on the viscosity of lecithin sol than any other salts, except iodides containing traces of free iodine. This seemed to suggest that the specific effect of bromides is not due to the bromide ions, but to free bromine. Pauli [1929] has pointed out the possibility of such a mechanism, and recent work of Lanza [1931] has proved that the addition of iodine to KI does not change the molecular concentration and onlyvery slightly affects the electrolytic dissociation of the latter. Owing to the unsaturated fatty acid content of lecithin a reaction with bromine or iodine is possible. As there is chemical evidence that fatty acids add KI, too, and are then enabled to bind more of other substances, even the behaviour of the compounds of lecithin and protein can be explained in this way. In order to test this hypothesis, the following series of experiments was made. Though egg-lecithin (Merck) is, according to Remesow [1930], far from pure, it was used, since most work has been done on it, and results permitting comparison with the latter were needed. The lecithin sol was made according to Keeser [1924] by adding small portions of boiling alcoholic solution of lecithin to boiling redistilled water. Some figures concerning the conductivity and cH of such sols are reported in Table IV. In order to check the possible influence of traces of alcohol, emulsions of lecithin in redistilled water were used in several experiments. Such emulsions [cf. Thomas, 1915], are more opaque than a fresh sample of a so] made after Keeser, but are nevertheless stable. The protein used consisted of serum-albumin and pseudoglobulin prepared from horse-serum by (NH4)2504 fractionation, and purified by reprecipitation, dialysis and electrodialysis.
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