Polysaccharides and other Macromolecules 4. THE OSMOTIC PRESSURE OF MIXTURES OF SERUM ALBUMIN AND HYALURONIC ACID* BY T. C. LAURENT

Ogston & Phelps (1961) found that hyaluronic acid markedly affects the partition of diffusible macromolecules between solutions of the polysaccharide and buffer. The authors explain the phenomenon as a steric exclusion of macromolecular solutes from solutions containing randomly coiled hyaluronic acid chains. From these results one can expect that hyaluronic acid and similar substances would exert a significant influence on the thermodynamic properties of solutions containing other macromolecules. The investigation reported in the present paper shows that solutions containing both hyaluronic acid and serum albumin have osmotic pressures in excess of the sum of osmotic pressures of solutions containing hyaluronic acid and serum albumin separately at the same concentrations. The influence of the 'effective volume' of a solute of finite concentration on the osmotic pressure of a solution has been treated by a number of authors (see, for example, Scatchard, 1946; Doty & Edsall, 1951; Edsall, 1953; Flory, 1953). Christiansen (1960), using the experimental results of Jensen & Marcker (1958), discussed the phenomenon in hyaluronic acid solutions. All these treatments, however, have been limited to the problem of binary systems containing the solvent and a single species of macromolecules. Ogston (1962) discussed from a theoretical point of view the thermodynamic properties of ternary systems with special reference to buffer solutions containing hyaluronic acid and serum albumin. The study of this problem was approached independently by the present authors. Experimental work was planned and carried out by one of us (T. C. L.) and a theoretical treatment of the thermodynamic properties of systems containing hyaluronic acid and serum albumin was made by the other (Ogston, 1962). The present paper combines the two approaches.