Osmotic Pressure, Molecular Weight, and Stability of Serum Albumin”

Because of the discrepancies at the time this investigation was begun in the estimates of t’he molecular weight of serum albumin, as made by Siirensen (1) (45,000) and hdair (2) (62,000) by means of osmotic pressure experiments, and by Svedberg and Sjiigren (4) (67,500) from ultracentrifugal measurements, the osmotic pressure of this protein was reinvest’igated under more suitable experimental conditions both in aqueous solution and certain mixed solvents, especially urea solutions. The molecular weight estimates of serum albumin reported here are in good agreement with those given in the more recent paper of Adair and Robinson (4), which became available short.ly after the completion of the major portion of the experimental part of this paper. Serum albumin is denatured by urea. Comparison of osmotic pressure measurements in aqueous and in urea solut’ions under similar experimental conditions makes it possible to consider whether changes in molecular weight accompany the process of denaturat#ion of this protein. ‘The recent investigations of Hopkins (5) have shown that the denaturation of certain proteins by urea is accompanied by changes in the sulfur linkages of t’he protein molecule.