Ultracentrifugal studies of rat, rabbit and guinea-pig serum albumins

Abstract

Albumins have been prepared from rat, rabbit and guinea-pig sera by trichloroacetic acid-ethanol and tartaric acid-methanol systems as well as by free electro-phoresis. Salt fractionation with magnesium sulphate was sometimes used in conjunction with these methods. The molecular weights of all these albumins, measured near neutrality in the ultracentrifuge, were close to 65,000. Differences were due to a combination of random error and the residual small amounts Of globulins. There was no demonstrable effect of freeze-drying on the molecular weights. The pH-dependence of S20, w for rat and rabbit albumins was closely similar to that for bovine,''human and horse albumins, S20 w falling steadily from about pH 5 to pH 2. The effect of variations ''in the environment indicated that electrostatic factors were implicated. The pH-depend-ence of S20 w for guinea-pig albumin involved a steady fall below pH 5, interrupted''by a large increase between approximately pH 3.6 and 3.2. This was shown to be due to dimer formation, but there was not sufficient information to reveal the details of this process.