Isolation and purification of human blood plasma proteins able to form potassium channels in artificial bilayer lipid membrane

A protein fraction able to induce K⁺-selective transport across a bilayer lipid membrane was isolated from human blood plasma with the use of the detergent- and proteolytic enzyme-free method developed in our laboratory. After addition of the studied sample to the artificial membrane in the presence of 100 mM KCl, a discrete current change was observed. No channel activity was recorded in the presence of calcium and sodium ions. Channel-forming activity of the fraction was observed only in the presence of K⁺. Using a threefold gradient of KCl in the presence of studied proteins, a potassium-selective potential balanced by voltage of ?29 mV was registered. This value is very close to the theoretical Nernst potential in this case. This means that the examined ion channel is cation-selective. According to the data obtained with MS-MALDI-TOF/TOF and NCBI database, three protein components were identified in the isolated sample.