Rat plasma selenoprotein P properties and purification.

Area of Science:

• Biochemistry
• Proteomics
• Trace Element Metabolism

Background:

• Selenoprotein P (SeP) is a key selenium-transporting protein in plasma.
• Understanding SeP's structure and selenium incorporation is crucial for selenium metabolism research.

Purpose of the Study:

• To isolate and characterize selenoprotein P from rat plasma.
• To determine the molecular weight and subunit composition of SeP.
• To investigate the distribution of selenium within the SeP molecule.

Main Methods:

• Rats were injected with 75SeO3(2-), and plasma was collected.
• Fractionation involved salt precipitation, Affi-Gel Blue, and DEAE chromatography.
• Purification of the 75Se-containing subunit utilized SDS-polyacrylamide gel electrophoresis and electroelution.
• Characterization included molecular weight determination, isoelectric focusing, and peptide mapping via reverse-phase HPLC and Sephadex G-50 chromatography.

Main Results:

• Selenoprotein P was identified as the primary 75Se-labeled protein in rat plasma.
• A 57 kDa 75Se-containing subunit was purified to 90% homogeneity with an 850-fold increase.
• The native molecular weight of SeP was determined to be 98,000, with a subunit isoelectric point at pH 5.4.
• Tryptic peptide analysis revealed that 75Se is distributed across multiple locations within the 57 kDa subunit.

Conclusions:

• The study successfully isolated and characterized the 75Se-containing subunit of rat selenoprotein P.
• Selenium is incorporated into multiple sites within the 57 kDa subunit of SeP.
• These findings contribute to understanding selenium transport and metabolism in mammals.