Montmorillonite as a Caliper for the Size of Protein Molecules

Abstract

IT is known that proteins may be adsorbed from solution by the clay montmorillonite, leading to an increase in d(00l) crystallographic spacings¹. In order to compare these increases with the size of protein molecules one must be certain that a complete mono-molecular layer of protein has been adsorbed, and this can be calculated to require 1.3–2.0 gm. of protein per gm. of clay. As the clay becomes saturated the adsorption isotherm levels off, but the isotherms are initially steeper than curves of the Langmuir type². Assuming that protein molecules are spherical, we have calculated the expected d(001) spacings and compared them with the experimental values found (Table 1). The agreement is moderately good for all but pepsin. Hæmoglobin appears to be adsorbed as a monomer, whereas lactoglobulin enters the clay particles as a dimer.