Ramasamy M, Alpers D H, Saxena V, Seetharam B
Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA.
J Nutr Biochem. 1990 Apr;1(4):213-9. doi: 10.1016/0955-2863(90)90110-7.
Plant lectins have been thought to impair nutrient absorption, both by specific and nonspecific interference in the absorptive process. The main objective of this investigation was to study the effect of lectins on the various binding reactions involving cobalamin (cbl)-protein complexes and their receptors, and to identify the rate-limiting step important in maintaining tissue levels of cobalamin. Among the lectins tested in vivo, only concanavalin A (ConA) was able to inhibit the transport of cobalamin to the tissues and caused a 70% to 75% inhibition of [(57)Co] cobalamin transported to the liver and kidney. The inhibition of transport to the tissues was independent of route of administration of cobalamin, whether intragastric or systemic, and was not due to decreased gastrointestinal uptake. When tested in vitro, concanavalin A inhibited the binding of transcobalamin II-cbl to its receptor, but not the binding of cobalamin to intrinsic factor or intrinsic factor-cobalamin complex to the ileal receptor. These results suggest that late events during transcellular transport of cobalamin through the enterocytes is the rate-limiting step determining tissue levels of cobalamin and that ConA inhibits these latter events.
植物凝集素被认为会通过对吸收过程的特异性和非特异性干扰来损害营养物质的吸收。本研究的主要目的是研究凝集素对涉及钴胺素（cbl）-蛋白质复合物及其受体的各种结合反应的影响，并确定维持组织中钴胺素水平的限速步骤。在体内测试的凝集素中，只有伴刀豆球蛋白A（ConA）能够抑制钴胺素向组织的转运，并导致转运到肝脏和肾脏的[（57）Co]钴胺素受到70%至75%的抑制。向组织转运的抑制与钴胺素的给药途径无关，无论是胃内给药还是全身给药，且不是由于胃肠道摄取减少所致。在体外测试时，伴刀豆球蛋白A抑制转钴胺素II-cbl与其受体的结合，但不抑制钴胺素与内因子或内因子-钴胺素复合物与回肠受体的结合。这些结果表明，钴胺素通过肠细胞进行跨细胞转运过程中的后期事件是决定组织中钴胺素水平的限速步骤，且ConA抑制了这些后期事件。
