The macromolecular properties of blood-group substances. Sedimentation-velocity and viscosity measurements.

1. Sedimentation-velocity, intrinsic-viscosity and partial-specific-volume measurements on a typical blood-group-specific glycoprotein are reported for a range of environmental conditions. 2. The sedimentation coefficients, S, are strongly concentration-dependent, and follow the reciprocal law; the limiting values at 2 degrees , 25 degrees and 45 degrees , after correction to 25 degrees , show slight dependence on temperature. 3. The intrinsic viscosities, [eta], at 25 degrees and 45 degrees show more marked temperature-dependence, and correspond to a very asymmetric or very expanded molecular conformation. 4. From the value of the ratio K/[eta], where K=S(0).d(1/S)/dc, it is concluded that the molecular conformation is roughly spherical; application of the Einstein viscosity equation then suggests an expansion factor of about 60, compatible with a flexible configuration approaching that of a random coil. 5. The sedimentation coefficient is not affected by variation of ionic strength in the range 0.01-0.50, nor by pH in the range 3-10. 6. Sodium dodecyl sulphate at 1.5% produces a small decrease in S; the effect is greater than would be expected from the observed extent of binding, but is too small to correspond to a significant change in secondary structure; the serological activity is unaffected by sodium dodecyl sulphate. 7. All the properties observed indicate the absence of any secondary structure in blood-group substances.