Automated system for determining the molecular weight and/or concentration of macromolecules via sedimentation equilibrium

摘要

An automated system for measuring the concentration gradient of centrifuged solute and directly calculating the molecular weight and/or sedimentation coefficient of an optically absorbing solute. Monochromatic light passes through a stationary slit and a previously centrifuged sample in a tube while the tube is moved vertically at a uniform rate by a platform which is driven by a motor and gearing, including a gear nut which drives a vertical screw attached to the platform. The transmitted light impinges on a photodetector which provides absorbance readings. This provides data of absorbance vs. time through the scanning cycle, which is processed digitally. A microcomputer is used to calculate the molecular weight and/or sedimentation coefficient from this data. The centrifuge tube is supported in a transparent cuvette containing a black plastic adaptor block which conformably receives the tube and supports it in upright position, allowing the light beam to pass through opposite vertical slot portions in the block. The cuvette rests on the platform, which is moved vertically relative to the slit defining the fixed beam path. A microswitch is operated at the upper limit of travel to stop the drive motor. The motor is external to the housing in which the optical components and the sample tube are located. The external motor is coupled by a flexible shaft to the drive gearing. Alternatively, a stepping motor may be employed instead of a synchronous motor to move the centrifuge tube in an incremental fashion rather than at uniform velocity.