Volume

A peptide’s volume can be estimated from the molecular weight of the peptide and an average protein partial specific volume. The partial specific volume of a protein is ratio between its volume and molecular weight.

Assumptions:

The average of experimentally determined partial specific volumes for soluble, globular proteins is approximately 0.73 cm³/g (average of experimental values from 13 soluble proteins). This value varies from protein to protein, but the range is rather narrow, between 0.70 and 0.75 cm³/g.

The simple calculation starts from

0.73 cm³/g x 10²⁴A/cm³ x molecular weight g/mole

6.02 x 10²³ molecules/mole

and results in a protein volume of approximately:

(1.21 x MW) A³/molecule

This provides a reasonable estimate for general uses. A recent reference concerning partial specific volumes is: Harpaz, Gerstein and Chothia (1994) Structure 2, 641-649 (issue of July 15).