The structure of rat proalbumin

Area of Science:

• Biochemistry
• Molecular Biology
• Proteomics

Background:

• Serum albumin is a major plasma protein.
• Proalbumin is a precursor form of serum albumin found in the liver.

Purpose of the Study:

• To determine the structure of rat proalbumin.
• To elucidate the relationship between proalbumin and rat serum albumin.

Main Methods:

• Edman degradation for N-terminal sequencing.
• Cyanogen bromide fragmentation for peptide analysis.
• Gel filtration, electrofocusing, and ion exchange chromatography for peptide separation.
• Amino acid and radiochemical sequence analysis.

Main Results:

• Rat proalbumin consists of a hexapeptide (Arg-Gly-Val-Phe-Arg-Arg) attached to the N-terminus of rat serum albumin.
• Cyanogen bromide treatment yielded peptides of 30,000, 10,000, and ≤5,000 molecular weights.
• The 10,000 MW fraction was identified as the N-terminal fragment of rat serum albumin.
• Limited tryptic hydrolysis released the N-terminal hexapeptide from proalbumin, resulting in a protein indistinguishable from rat serum albumin.

Conclusions:

• The N-terminal hexapeptide is the distinguishing feature of rat proalbumin compared to rat serum albumin.
• Proalbumin is processed into serum albumin via the removal of this N-terminal hexapeptide.