[Autocalibration method of sedimentation equilibrium for determining the molecular weight of proteins. Ideal solutions].

The theory underlying the autocalibration method of sedimentation equilibrium for ideal solutions and its experimental verification for isolated proteins and a mixture of two proteins are described. The method is based on simultaneous calculation of an invisible base level yg which is to be known for calibration of sedimentation equilibrium patterns and parameter q = M (1--upsilon rho) omega 2/RT. It is shown that owing to this "autocalibration" the accuracy of molecular weight measurements increases to about 1% for homogeneous proteins and to 3--4% for mixtures of two proteins. Thus there is no need either in "meniscus depletion" as in the case of a "high speed" equilibrium method, or in determination of C0 and solute preservation in the cell ("low speed" method). The speed may be so low that the optical distortions would be minimized, the initial concentration may be varied over a wide range from approximately 0.1 mg/ml and higher (with interference optics). The autocalibration method allows one to repeat the calculations on intervals truncated from the bottom and from the meniscus, which ensures a good estimation of the homogeneity of the solution.