UPTAKE AND METABOLISM OF BIOTIN BY HUMAN PERIPHERAL-BLOOD MONONUCLEAR-CELLS

We studied the uptake of biotin into human peripheral blood mononuclea r cells (PBMC) using [H-3]biotin and studied the catabolism of biotin in PBMC using [C-14]biotin. Over 30 min, [H-3]biotin uptake was greate r at 37 degrees C than at 25 degrees C (K-T = 2.6 +/- 0.4 nM, maximal velocity = 2.9 +/- 0.2 fmol.10(6) cells(-1).30 min(-1)). Ouabain reduc ed [H-3]biotin uptake to 65% of control values, suggesting that biotin uptake is Na-K-ATPase dependent. Unlabeled biotin and biotin analogs reduced the uptake of [H-3]biotin to 22-70% of control values, suggest ing the presence of a competition for a structurally specific biotin t ransporter When endocytosis by PBMC was stimulated by various acyl gly cerols, [3H]biotin uptake was 40-73% of control values; these data are consistent with the hypothesis that stimulated endocytosis reduces bi otin transporter density on the cell surface. During a 168-h incubatio n, PBMC did not catabolize [C-14]biotin.