retinol-phosphate and retinol-palmitate

In the present study the effect of retinoids on the membrane form of galactosyltransferase was tested. A model system consisting of pure bovine milk galactosyltransferase and phosphatidylserine vesicles was used for this investigation. Retinol, retinal and retinylphosphate were able to overcome the modulating effect of phosphatidylserine, that is, activated the enzyme. Retinoic acid and retinylpalmitate were ineffective in this system.

Topics: Animals; Cattle; Diterpenes; Female; Galactosyltransferases; Kinetics; Liposomes; Milk; Phosphatidylserines; Retinaldehyde; Retinoids; Retinyl Esters; Vitamin A

Regulation of the biosynthesis of alpha-fetoprotein and albumin was studied in a temperature-sensitive fetal rat hepatocyte line (RLA209-15) which exhibits a differentiated phenotype when grown at 40 degrees C. Retinoic acid inhibited alpha-fetoprotein production but increased albumin production. This retinoid also changed the proportion of three forms of alpha-fetoprotein; the biosynthesis of the 73,000- and 69,000-dalton variants, which are indistinguishable from authentic rat alpha-fetoprotein, was inhibited and an additional 65,000-dalton variant was induced. It has previously been shown that alpha-fetoprotein production decreases during maturation whereas albumin production increases. Our data suggest that retinoic acid induces maturation of fetal liver cells in vitro. Further, the 65,000-dalton alpha-fetoprotein variant may be characteristic of liver maturation.

Topics: alpha-Fetoproteins; Animals; Cell Line; Diterpenes; Fetus; Kinetics; Liver; Rats; Retinyl Esters; Serum Albumin; Tretinoin; Vitamin A

The retinyl palmitate content of the postnuclear membrane fraction from 10 Morris hepatomas, their host rat livers, one acetylaminofluorene-induced rat liver hepatoma, and the host liver and of regenerating rat liver was measured by reverse-phase high-pressure liquid chromatography of the chloroform:methanol extracts. Membranes from the hepatoma tissue contained less than detectable levels of retinyl acyl esters, whereas membranes from host liver tissue and regenerating liver contained levels of retinyl palmitate within normal ranges. The amount of cellular retinol-binding protein was also decreased considerably in cytosols from 9618 and 7777 hepatomas. The ratio of endogenous retinyl phosphate to the polyisoprenoid dolichyl phosphate available for mannosylation in an assay containing postnuclear membranes and guanosine dephospho[14C] mannose was decreased by a factor of 3 to 10 in hepatoma tissue. Such change in ratio was not attributable to specific changes in retinyl phosphate mannose-synthesizing activity, but it appeared to be related to the vitamin A deficiency condition of the membrane from tumors. As for membranes from vitamin A-deficient liver tissue, postnuclear membranes from rat cystic hepatocarcinoma, Morris 7777, 3924A1-1, and 5123D-1-2 transplantable rat hepatomas and guinea pig line 10 hepatoma all synthesized a mannolipid with intermediate hydrophobic properties between retinyl phosphate mannose and dolichyl phosphate mannose and not normally found in liver tissue. These alterations in patterns of lipid intermediates may be responsible for altered glycosylation of glycoproteins in neoplastic cells. In conclusion, the present investigation establishes that hepatoma cell membrane is in a status of vitamin A and of retinyl phosphate depletion, while dolichyl phosphate contents appear similar to host liver membrane.

Topics: Animals; Carbon Radioisotopes; Cell Membrane; Diterpenes; Dolichol Phosphates; Guinea Pigs; Liver; Liver Neoplasms, Experimental; Liver Regeneration; Male; Polyisoprenyl Phosphates; Rats; Rats, Inbred BUF; Retinyl Esters; Vitamin A