Moe A J, Plas D R, Powell K A, Smith C H
Edward Mallinckrodt Department of Pediatrics, Children's Hospital, Washington University School of Medicine, St Louis, MO 63110.
Placenta. 1994 Feb-Mar;15(2):137-46. doi: 10.1016/s0143-4004(05)80450-3.
Riboflavin uptake was characterized using membrane vesicles isolated from the apical (maternal-facing) and basal (fetal-facing) membranes of the syncytiotrophoblast from full-term human placentas. Equilibrium [3H]riboflavin uptake was insensitive to variations in incubation medium osmolarity in contrast to [3H]alanine uptake into an osmotically sensitive space. Osmotic insensitivity suggested riboflavin binding to a membrane component. The dissociation constant of riboflavin binding was similar in microvillous (Kd = 2 microM) and basal membrane vesicles (Kd = 1 microM). Binding capacity was significantly higher in microvillous membranes (Bmax = 11.9 pmol/mg protein). The relatively high affinity binding to the membrane vesicles may represent a first step in riboflavin transport.
使用从足月人胎盘合体滋养层的顶端（面向母体）和基底（面向胎儿）膜分离的膜囊泡对核黄素摄取进行了表征。与[³H]丙氨酸摄取到对渗透压敏感的空间不同，平衡[³H]核黄素摄取对孵育培养基渗透压的变化不敏感。渗透压不敏感性表明核黄素与膜成分结合。核黄素结合的解离常数在微绒毛膜囊泡（Kd = 2 microM）和基底膜囊泡（Kd = 1 microM）中相似。微绒毛膜中的结合能力显著更高（Bmax = 11.9 pmol/mg蛋白质）。与膜囊泡的相对高亲和力结合可能代表核黄素转运的第一步。
