Effects of Dietary-Fat Saturation on the Composition of Very-Low-Density Lipoproteins and on the Metabolism of their Major Apoprotein, Apolipoprotein B

binding isotherm in a single experiment. Both preparations contained a saturable component able to bind glycocholic acid although the number of sites in the ileal preparation (179pmol/g of supernatant protein) was greater than that in the jejunal preparation (47,umol/g of supernatant protein). The similarity between the value for the dissociation constant of the ileal component (2.5pmol/l) and that of the jejunal component (1.6pmoI/l) suggests that it may be the same component that is present in different concentrations in both preparations. Previous studies identified two proteins in liver supernatants able to bind bile acids. Both these proteins possessed glutathione S-transferase activity and one was provisionally identified as the non-specific anion-binding protein ligandin (glutathione S-transferase B) (Strange et al., 19776). In contrast with the bile-acid-binding proteins found in liver, the binding component of mol.wt. approx. 40000 found in the small intestine did not possess glutathione S-transferase activity and unlike ligandin was not retained by CM-Sephadex. The terminal ileum is quantitatively an important site of bile-acid transport and the function of the soluble protein may be to ensure that the intracellular concentration of free bile acid remains small.