The Acid-, Base-, and Salt-binding Capacity of Salt- Denatured Collagen

Theis and Steinhardt (1) recently have shown that, when native collagen is treated with calcium or magnesium chloride solutions, drastic shrinkage of the collagen occurs at low temperatures. It was further shown that potassium or sodium chloride has exactly the reverse effect; i.e., they actually increase the temperature at which collagen is said to contract. The effect of neutral salts upon the acidor base-binding power of proteins has been rat,her extensively studied but the available literature contains some rather conflicting data. Csapo (2) in 1925 found that the presence of salt influenced the combination of the proteins with acids or bases. Gerngross and Loewe (3) found increased fixation of alkali by hide powder upon addition of neutral salt. Reiner (4) suggested that the salt effect was apparent rather than real and that if allowance was made for the protein influence upon other salt ions the alkali fixed would be found to be the same in the presence or absence of salts. Cohn, Green, and Blanchard (5) indicat)ed the titration curve was shifted, in the presence of salts, on both sides of the isoelectric point but that the total amount of acid or base fixed was unaffect,ed. Atkin and Campos (6) made use of the presence of potassium chloride in estimating the acidand base-binding capacity of collagen, postulating that the neutral salt is necessary for equalizing the internal pH within the protein with that of the external solution. Steinhardt and Harris (7) and Theis and Jacoby (8) investigated the effect of solutions of potassium chloride of various ionic strengths upon the acidand base-binding power of fibrous proteins and found that the neutral salt affected the slope of the titration curve on each side of the isoionic point but did not affect either the maximum acidor base-binding power or the position of the isoionic point of the given protein. Cannan in 1938 (9) showed that the titration curves shift in the presence of salt) and also appear to pivot around the isoionic point,. Later, Cannan, Kibrick, and Palmer (10) found by substituting calcium chloride for the potassium salt that the only observable effect was a displacement of the titration curve toward a lower pH, to an extent increasing with ionic strength. They found the displacements caused by Ca++ and Mg++ ions to be identical but greater than those due to Sr++ and Ba++ ions.