CHEMICAL, CLINICAL, AND IMMUNOLOGICAL STUDIES ON THE PRODUCTS OF HUMAN PLASMA FRACTIONATION. VI. THE OSMOTIC PRESSURE OF PLASMA AND OF SERUM ALBUMIN 12

Abstract

The osmotic pressures of plasma and of serum albumin at 25[degree] have been measured over ranges of conc. and pH, much wider than the physiological ranges. The extrapolation of the osmotic pressure-conc. ratio to zero conc. yields a molecular wt. of 69,000 for albumin. A similar extrapolation for plasma yields an avg. molecular wt. of about 90,000. This corresponds to an avg. wt. of about 170,000 for the 40% of the protein which is not albumin. The osmotic pressure[long dash]conc. ratios increase rapidly with increasing cone. At pH 7.4, this increase corresponds to the Donnan effect of the ionic charges, but measurements over a pH range show this to be a coincidence. The vol. of blood held by a g. of albumin is about 18 ml. and varies with the protein content of the plasma. Each gram of albumin is equivalent to 1.2 gs. of plasma protein or 20 ml. of the current Red Cross citrated, pooled plasma.