Multiple forms of albumin and their conversion from pro-type to serum-type in rat liver in vivo.

Purified rat serum albumin was resolved into five forms by polyacrylamide gel isoelectric focusing, while albumin isolated from the subcellular fractions of rat liver consisted of those of serum albumin and four additional forms. This latter four forms were identified as proalbumin, since they were converted to those of serum albumin by limited proteolysis with trypsin. This method was applied to the determination of the conversion site of proalbumin in the liver, revealing that substantial conversion of proalbumin occurs in the Golgi cisternae as well as in the secretory vesicles.