Liquid–vapor interfacial tension of blood plasma, serum and purified protein constituents thereof

A systematic study of water–air (liquid–vapor, LV) interfacial tension γlvγlv of blood plasma and serum derived from four different mammalian species (human, bovine, ovine and equine) reveals nearly identical concentration-dependence (dγlvdlnCB; where CB is plasma/serum dilution expressed in v/v concentration units). Comparison of results to a previously-published survey of purified human-blood proteins further reveals that dγlvdlnCB of plasma and serum is surprisingly similar to that of purified protein constituents. It is thus concluded that any combination of blood-protein constituents will be substantially similar because dγlvdlnCB of individual proteins are very similar. Experimental results are further interpreted in terms of a recently-developed theory emphasizing the controlling role of water in protein adsorption. Accordingly, the LV interphase saturates with protein adsorbed from bulk solution at a fixed weight-volume concentration (∼436 mg/mL) independent of protein identity or mixture. As a direct consequence, dγlvdlnCB of purified proteins closely resembles that of mixed solutions and does not depend on the relative proportions of individual proteins comprising a mixture. Thus variations in the plasma proteome between species are not reflected in dγlvdlnCB nor is serum different from plasma in this regard, despite being depleted of coagulation proteins (e.g. fibrinogen). A comparison of pendant-drop and Wilhelmy-balance tensiometry as tools for assessing protein γlvγlv shows that measurement conditions employed in the typical Wilhelmy plate approach fails to achieve the steady-state adsorption state that is accessible to pendant-drop tensiometry.