Measurements of Very Small Osmotic Pressures of the Haemocyanin of Pila leopoldvillensis

Abstract

OSMOTIC pressure measurements of solutions of Pila haemocyanin have been made with a toluene osmometer provided with a siphon tube¹. With this apparatus, after osmotic equilibrium has been attained, the manometer can be connected with the dialysate by opening a screw-clamp, to give a reading of zero pressure. After reclosing the clamp and allowing osmotic equilibrium to be established again, a second reading of the osmotic pressure can be taken, and these procedures can be repeated as often as is required. If the molecular weight of the protein is to be calculated from osmotic pressure determinations, it is desirable to include measurements made on dilute protein solutions. A reading microscope has been used for measurements from 0.13 to 3 mm of toluene. Maximum and standard errors of readings are recorded in Table 1, together with osmotic pressures observed for solutions of haemocyanin equilibrated at 1° C with acetate buffers of ionic strength 0.15 and pH 5.2 and 5.94 and of ionic strength 0.02 and pH 5.90.