Said H M, Thuy L P, Sweetman L, Schatzman B
Medical Research Service, VA Medical Center, Long Beach, California.
Gastroenterology. 1993 Jan;104(1):75-80. doi: 10.1016/0016-5085(93)90837-3.
Biocytin is an important end product of intraluminal digestion of dietary protein-bound biotin. Limited studies are available regarding the ability of the small intestine to transport biocytin and about the mechanism involved. The aim of the present study was to delineate these issues.
Transport of [3H]-biocytin was examined using everted sacs from rat intestine.
Mucosal-to-serosal transport of low (0.022 mumol/L) and high (5 mumol/L) concentrations of biocytin were linear for up to 20 minutes of incubation. Transport of biocytin as a function of concentration (0.022-5 mumol/L) was linear (r = 0.99) and occurred at a rate of 22,062 fmol.g tissue (wet wt)-1.15 min-1. Addition of high concentrations of unlabeled biocytin, biotin, biotin methyl ester, and lysine did not cause a significant inhibition of the transport of [3H]-biocytin. Furthermore, transport of biocytin was independent of Na+ concentration, pH, energy, and temperature. Compared with transport of equimolar concentrations of free biotin, transport of biocytin (0.022 mumol/L) was significantly lower in both the jejunum and the ileum.
(1) Biocytin transport in rat intestine is lower than that of free biotin and occurs via simple physical diffusion. (2) In the rat, efficient absorption and optimal bioavailability of dietary protein-bound biotin necessitates its conversion to free biotin.
生物胞素是膳食中蛋白质结合型生物素腔内消化的重要终产物。关于小肠转运生物胞素的能力及其相关机制的研究有限。本研究旨在阐明这些问题。
使用大鼠肠外翻囊研究[3H] - 生物胞素的转运。
低浓度（0.022 μmol/L）和高浓度（5 μmol/L）生物胞素的黏膜到浆膜转运在孵育长达20分钟时呈线性。生物胞素的转运作为浓度（0.022 - 5 μmol/L）的函数呈线性（r = 0.99），转运速率为22,062 fmol·g组织（湿重）-1·1.15分钟-1。添加高浓度的未标记生物胞素、生物素、生物素甲酯和赖氨酸不会显著抑制[3H] - 生物胞素的转运。此外，生物胞素的转运与Na + 浓度、pH、能量和温度无关。与等摩尔浓度的游离生物素的转运相比，空肠和回肠中生物胞素（0.022 μmol/L）的转运均显著较低。
（1）大鼠肠道中生物胞素的转运低于游离生物素，且通过简单的物理扩散发生。（2）在大鼠中，膳食中蛋白质结合型生物素的有效吸收和最佳生物利用度需要将其转化为游离生物素。
