To facilitate sedimentation equilibrium experiments on the model E analytical ultracentrifuge, a method for automated data acquisition from the photoelectric scanner system has been developed. The instrumentation described is relatively simple to install and convenient to operate. Direct access to computer analysis of data is thus achieved. Application is made to the study of a protein, allophycocyanin. Results over a range of pH and protein concentrations confirm that an a& structure is stable in aqueous media.
An analytical ultracentrifuge equipped with a photoelectric scanner is useful in obtaining molecular weights of dilute solutions in sedimentation equilibrium experiments. The standard commercially available instrument (Beckman Model E) displays data on a recorder in the form of a position versus absorbance curve. The manual determination of the coordinates from this curve effectively limits the precision ofthe calculated results. The data reduction calculations are extensive and the use of programmable calculators or computers is standard procedure. However, the manual entry of the data can be a tedious procedure and is a source of errors.
Automation of the data handling procedures has been proven feasible in earlier studies. Woods er al. (1) developed a system where the analog signal from the ultracentrifuge is recorded on magnetic tape. From this magnetic tape a paper tape is created containing the data in digitized form which is ultimately read and analyzed by a computer. As these authors (1) indicated, this system is overly complex and expensive since an intermediate magnetic tape is generated rather than directly creating the paper tape of digitized information.
Crepeau et nl. (2,3) constructed an on-line system where the photomultiplier pulses are directed to an analog-to-digital (A/D) converter and then to a dedicated minicomputer for analysis. The digitized data are permanently stored on magnetic tape cassettes. This system has the