Serum albumin, the main protein of plasma, has a good binding capacity for water, Ca(2+), Na(+), K(+), fatty acids, hormones, bilirubin and drugs. Its main function is the regulation of the colloidal osmotic pressure of blood. Plasma. Adults. In the sea lamprey, there are two forms of albumin, AS and SDS-1. Belongs to the ALB/AFP/VDB family.