Compressibility studies of three proteins in CsCI solutions in the analytical ultracentrifuge

✍ Scribed by Dan S. Sharp; Norman Fujita; Kathleen Kinzie; James B. Ifft

• Book ID: 102761660
• Publisher: Wiley (John Wiley & Sons)
• Year: 1978
• Tongue: English
• Weight: 1013 KB
• Volume: 17
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1978.360170402

✦ Synopsis

The compositional buoyant densities, p8, of human y-immunoglobulin, bovine serum mercaptalbumin, and egg albumin have been measured in CsCl solutions in the analytical ultracentrifuge as a function of pressure. Standard pressure coefficients, $0, and standard partial specific volumes of the solvated proteins, i T: , o, have been computed from these data. The values obtained are strikingly different from each other and from the only other pressure coefficients which have been measured, those values obtained for nucleic acids and nucleoproteins. The $O value for y-immunoglobulin is negative, the first nonpositive value obtained, and suggests an unusual internal structure for this protein. The pressure coefficient of mercaptalbumin is not constant. A second-order relation is derived and utilized to interpret these data. The slope of the pg(P) plot for egg albumin was constant and negative and yielded values of $O which are about 20% as large as those reported for DNA. Evaluation of published isopiestic data for egg albumin in CsCl solutions provided the dependence of preferential hydration on water activity. This quantity, (dr'lda?), as well as a, were found to be negative. The values of,$O and a were used to compute the effective density gradient from which the correct molecular weight of egg albumin was obtained. The apparent specific volume of egg albumin in a buoyant CsCl solution was measured using the Mettler-Paar densimeter.