consequence of the close packed interior of proteins is that all
proteins have approximately the same density, about 1.37 g/cm^3.
For most of the following, [researchers] will use the partial specific volume,
v2, which is the reciprocal of the density. v2 varies from 0.70 to
0.76 for different proteins, and there is a literature on calculating
or determining the value experimentally. For the present discussion,
[researchers] will ignore these variations and assume the average v2=