Factors responsible for the high lipogenic activity of rabbit serum were investigated using an assay procedure based on the gravimetric determination of the 24 hr increase in cell lipid. Cellular synthesis of @entity1718 was inhibited by the presence of serum in the assay medium. Approximately 90% of the increase in cell lipid produced by serum fractions was due to @entity412 accumulation. Fractionation of rabbit serum by precipitation with @entity1329 or by ultracentrifugation in high density medium, both indicated that three-quarters of its lipogenic activity was associated with albumin. The lipoproteins prepared by ultracentrifugation also exhibited about one-half the activity of whole serum. The lipogenic activity of albumin was confirmed by the high potency of the albumin isolated in a nearly pure form from proteins of d>1.21 by precipitation with @entity2804 and extraction with @entity1068 . As judged from chemical and isotopic analysis, neither the lipid content nor the lipid composition of the albumin was appreciably altered during its isolation. Of the albumin-bound lipids, only the free @entity1718 , as determined by @entity8851 column chromatography, were present in an amount sufficient to account for the observed increase in cell @entity1674 . In control experiments with horse serum of low lipogenic activity, the proteins of d>1.21 also possessed low activity in conjunction with a low content of free @entity844 . However, the albumin isolated from the latter preparation exhibited the high lipogenic activity of rabbit serum albumin. Chemical and isotopic analysis of the recovered horse serum albumin revealed that its free @entity844 content was the same as that of rabbit serum albumin. These results indicated that the isolation of horse serum albumin was attended by a substantial increase in its free @entity844 content. When the rabbit serum and horse serum content of media were adjusted to provide equivalent concentrations of albumin-bound @entity1718 , the @entity95 liver cells grown on the former media accumulated more lipid than cells grown on the latter media. This difference was shown to be due to the higher concentration of albumin per micro mole of @entity844 in horse serum as compared with rabbit serum. Consequently, the albumin to @entity844 ratio also controls the lipogenic activity of a serum. A linear relationship is presented which relates the cell lipid content to the molar ratio of albumin to free @entity1718 and to the absolute concentration of free @entity1718 in the medium.

Identification of albumin-bound XXXX as the major factor in serum-induced lipid accumulation by cultured cells.

@entity844 :: ('CHEBI:35366', 'Chemical') :: ['fatty acid'] @entity1674 :: ('MESH:D014280', 'Chemical') :: ['triglycerides'] @entity95 :: ('9986', 'Species') :: ['rabbit'] @entity1068 :: ('MESH:D000431', 'Chemical') :: ['ethanol'] @entity412 :: ('CHEBI:17855', 'Chemical') :: ['triglyceride'] @entity8851 :: ('MESH:C007369', 'Chemical') :: ['DEAE'] @entity1329 :: ('MESH:D000645', 'Chemical') :: ['ammonium sulfate'] @entity1718 :: ('MESH:D005227', 'Chemical') :: ['fatty acids'] @entity2804 :: ('MESH:D014238', 'Chemical') :: ['trichloroacetic acid']
@entity1718 :: (MESH:D005227,Chemical) :: ['fatty acids']
