Calculation and experimental verification of the frictional ratio of hagfish proteinase inhibitor

Abstract

A major structural feature of the alpha-2-macroglobulin-like inhibitor of hagfish described in Osada, Nishigai, and Ikai [(1987) J. Ultrastruct. Mol. Struct. Res. 96, 00-00] was its highly open quaternary structure observed under an electron microscope. We drew a qualitative conclusion that the high frictional ratio obtained from the result of sedimentation study and the large Stokes radius obtained in gel chromatographic experiment were the reflection of such an open quaternary structure. In this paper I present several structural models of hagfish inhibitor based on its electron micrographs and calculate expected frictional ratios for such models according to the method developed by Bloomfield and his co-workers. Their method allows the calculation of frictional coefficient of a body of an arbitrary shape by approximating it with a collection of small spheres. To test the validity of such a method, macroscopic models were built from plastic spheres or cylindrical capsules and their translational frictional coefficients were measured by the free-falling method under experimental conditions where the Reynolds number was between 10(-3) and 10(-4).