Apoproteins of the lipoproteins in a nonrecirculating perfusate of rat liver1

Abstract

The apoproteins of serum lipoproteins and of lipoproteins present in a nonrecirculating perfusate of rat liver were compared by immunochemical, gel electrophoretic, and solubility techniques. Serum and perfusate very low density lipoprotein apoprotein composition were not different. No evidence for the presence of a lipoprotein resembling serum low density lipoprotein was obtained. However, the apoprotein composition of circulatory high density lipoprotein was quantitatively different from the secretory product in the density 1.06–1.21 range. As measured by stained sodium dodecyl sulfate gel electrophoretic patterns, the arginine-rich protein was the major secretory apoprotein while the A-I protein was the major apoprotein in circulating high density lipoprotein. A very similar pattern was seen in perfusates of orotic acid-fatty livers. It was concluded that although the liver secrets lipoproteins in the high density class, circulatory high density lipoprotein is largely a product of catabolic processes.The arginine-rich protein was isolated from rat serum very low density lipoprotein by chromatography on an agarosesodium dodecyl sulfate column in one step, and shown to have a similar amino acid composition to that reported for this protein isolated from rat serum high density lipoprotein. When labeled amino acids were added to the perfusion medium, the arginine-rich protein had the highest apparent specific activity at 45 min and its specific activity was the same in high density lipoprotein as in very low density lipoprotein.

Keywords

• liver perfusion
• lipoproteins
• apoproteins