Summary
Electron microscopy and particle electrophoresis were found to be complementary techniques
with which to complete the physical data from an earlier study on barium sulphates
used to adsorb clotting factors from serum. The differences revealed by scanning electron
microscopy (S. E. M.) in the physical shape of low and high density grades of barium
sulphate particles appear to be of greater significance than charge as expressed by
electrophoretic mobility, in determining whether or not precursor or preformed factor
Xa is eluted.
This conclusion was based on the finding that at pH values close to 7, where the adsorption
from serum occurs, all samples with the exception of natural barytes were uncharged.
However as the high-density, or soil-grade, was found by S. E. M. to consist of large
solid crystals it was suggested that this shape might induce activation of factor
X as a result of partial denaturation and consequent unfolding of the adsorbed protein.
In contrast, uptake of protein into the centre of the porous aggregates revealed by
S. E. M. pictures of low-density or X-ray grade barium sulphate may afford protection
against denaturation and exposure of the enzyme site.
The porous nature of particles of low-density barium sulphate compared with the solid
crystalline forms of other grades accounts not only for its lower bulk density but
also for its greater surface/gram ratio which is reflected by an ability to adsorb
more protein from serum.
Neither technique produced evidence from any of the samples to indicate the presence
of stabilising agents sometimes used to coat particles in barium meals.
