Uptake and metabolism of biotin by human peripheral blood mononuclear cells.

We studied the uptake of biotin into human peripheral blood mononuclear cells (PBMC) using [3H]biotin and studied the catabolism of biotin in PBMC using [14C]biotin. Over 30 min, [3H]biotin uptake was greater at 37 degrees C than at 25 degrees C (KT = 2.6 +/- 0.4 nM, maximal velocity = 2.9 +/- 0.2 fmol . 10(6) cells-1 . 30 min-1). Ouabain reduced [3H]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 [3H]biotin to 22-70% of control values, suggesting the presence of a competition for a structurally specific biotin transporter. When endocytosis by PBMC was stimulated by various acyl glycerols, [3H]biotin uptake was 40-73% of control values; these data are consistent with the hypothesis that stimulated endocytosis reduces biotin transporter density on the cell surface. During a 168-h incubation, PBMC did not catabolize [14C]biotin.