The effect of the dipolar ions, @entity2228 , @entity28656 , and @entity68854 on the polymerization of @entity21104 ) protein has been studied by the methods of light scattering and ultracentrifugation. All three dipolar ions promote polymerization. The major reaction in the early stage is transition from the 4 S to the 20 S state. As in the absence of dipolar ions, the polymerization is enhanced by an increase in temperature; it is endothermic and therefore entropy-driven. The effect of the dipolar ions can be understood in terms of their action as salting-out agents; they increase the activity coefficient of @entity21104 A protein, the 4 S material, and thus shift the equilibrium toward the 20 S state. The salting-out constants, K, for the reaction in 0.10 ionic strength @entity1391 buffer at pH 6.7 was found by the light scattering method to be 1.6 for @entity2228 , 2.5 for @entity28656 , and 2.5 for @entity68854 . A value of 2.7 was obtained by the ultracentrifugation method for @entity28656 in @entity1391 buffer at 0.1 ionic strength and pH 6.8 at 10 degrees C. For both @entity2228 and @entity28656 , K increases when the ionic strength of the @entity1391 buffer is decreased. This result suggests that electrolytes decrease the activity coefficient of the dipolar ions, a salting-in phenomenon. However, the salting-in constants evaluated from these results are substantially higher than those previously determined by solubility measurements. The effect of @entity2228 and @entity28656 on polymerization was studied at pH values between 6.2 and 6.8. The effectiveness of both dipolar ions is approximately 50% greater at pH 6.8 than at pH 6.2. The variation of the extent of polymerization with pH in the presence of the dipolar ions is consistent with the interpretation that approximately one @entity3884 ion is bound for half of the polypeptide units in the polymerized A protein.

Effect of dipolar ions on the entropy-driven polymerization of XXXX protein.

@entity3884 :: ('MESH:D006859', 'Chemical') :: ['hydrogen'] @entity21104 :: ('12242', 'Species') :: ['tobacco mosaic virus (TMV', 'TMV'] @entity28656 :: ('MESH:D006033', 'Chemical') :: ['glycylglycine'] @entity2228 :: ('CHEBI:57305', 'Chemical') :: ['glycine'] @entity68854 :: ('MESH:C035647', 'Chemical') :: ['glycylglycylglycine'] @entity1391 :: ('CHEBI:26020', 'Chemical') :: ['phosphate']
@entity21104 :: (12242,Species) :: ['tobacco mosaic virus']
