Denaturation Changes in Egg Albumin with Urea, Radiation, and Heat by Janet H, Clark

The change produced in native proteins by various agents which results in loss of their characteristic properties and changes in solubility is called denaturation. The term, however, may be applied to structural and physical changes in the protein molecule which differ widely with the particular agent used. Urea denaturation differs in many respects from both heat and radiation denaturation. Urea has a strong dispersivO action on proteins so that when a high concentration of urea is added to a protein the solution remains clear until the solution is diluted or dialyzed when a certain amount of insoluble protein is formed. Hopkins (1) found that the rate of denaturation of egg albumin by urea varied inversely with the temperature, but Diebold (2) found a positive temperature coefficient for the denaturation of fibrinogen by urea. Owing to its dispersive action high concentrations of urea will dissolve proteins coagulated by the action of heat or radiation, or other denaturing agents. Laporta (3) reports a certain amount of reversal of denaturation as a result of this dispersion by urea. Steinhardt (4) has shown that the functional properties of hemoglobin and pepsin are retained in urea solution so that the loss of solubility after treatment with urea may not be a true denaturation. Many observers (2, 5, 6) have found that sulfhydryl groups appear after denaturation which are not detectable in native proteins. In the case of urea denaturation the number of SH groups is independent of the protein concentration and depends on the concentration of urea. In the presence of urea most proteins split into smaller molecules. Burk and Greenberg (7) found that in 40 per cent urea hemoglobin had half of its normal molecular weight but that egg albumin was unchanged. Recently Williams and Watson (8) found some dissociation of egg albumin into smaller molecules in 50 per cent urea. This investigation was undertaken with the idea of comparing the effect bf different denaturation agents on molecular structure and shape and of studying the interrelations between the effects of different denaturation agents. In the course of the study certain new observations on urea denaturation were made.