Differences in the Enzymatic Digestibility of the Variable and Constant Halves of Bence-Jones Protein with Temperature

A study of the limited peptic and tryptic fragmentation of intact type K Bence-Jones proteins into the variable and the constant halves showed a strong difference in the subsequent digestibility of the variable half and the constant half at different temperatures. The variable half was much more resistant to enzymatic digestion than the constant half at 37°, whereas the situation was reversed at 55°. This suggests that there is a larger contribution of hydrophobic bonds to the tertiary structure of the constant half than to the tertiary structure of the variable half and perhaps a greater contribution of salt linkages to the tertiary structure of the variable half. The temperature differential permits the easy preparation and isolation of the fragments of the variable and the constant halves since only the variable-half fragment and the remaining intact Bence-Jones protein are found in the digest after digestion at 37° and only the constant-half fragment is found after digestion at 55°.