Abstract
One of the interactions between macromolecules is the attractive force through the excluded volume effect. We studied the attraction between the molecules of muscle protein, actin, from the following two points by using the extended scaled particle theory (XSPT). I) we verified the basic assumption used in the XSPT that topological elements which determine the analytical expression of the excluded volume are almost unchanged through the scaling down of the solute molecule in the thought experiment. Results of the computational geometry method (α-shape method) showed that this assumption is valid even in the case of the actin molecule. II) we calculated the attraction between actin monomer molecules, G-actin. Calculated differences of the values of the attraction potential of two macromolecules between at contact and at one macromolecule apart by the XSPT is almost the same as those by the Asakura-Oosawa theory.
