A re-investigation of actin monomer conformation under polymerizing conditions based on rates of enzymatic digestion and ultraviolet difference spectroscopy.

There have been several reports which describe a conformational change of G-actin monomer in the presence of 0.1 M KCl. This altered monomer has been variously named, depending on whether the authors believed that it resembles G-actin, F-actin or has a conformation of its own. In this report we re-examine the experimental evidence for these proposals. The techniques include measurements of the rates of proteolytic digestion as well as near and far ultraviolet difference spectroscopy of actin in the presence and absence of KCl. We conclude that there is no compelling evidence for proposing a novel form of actin monomer.