Molecular weight and hydrodynamic properties of apolipoprotein B in guanidine hydrochloride and sodium dodecyl sulfate solutions.

The apolipoprotein B polypeptide of human serum low density lipoprotein exists (after reduction of disulfide bonds) as a random coil with a molecular weight of 250,000 in concentrated solutions of guanidine hydrochloride. With intact disulfide bonds, there is a limited restraint on the polypeptide conformation in this denaturing solvent. In the presence of saturating amounts of bound sodium dodecyl sulfate, the apolipoprotein is dimeric and highly asymmetric. This work substantiates the monomeric molecular weight of 250,000 for apolipoprotein B reported by others (Smith, R., Dawson, J.R., and Tanford, C. (1972) J. Biol. Chem. 247, 3376-3381) and demonstrates that the dimeric state of the polypeptide extant in vivo is maintained in micellar detergent solution.