Torras-Llort M, Soriano-García J F, Ferrer R, Moretó M
Unitat de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Spain.
Am J Physiol. 1998 Jan;274(1):R69-75. doi: 10.1152/ajpregu.1998.274.1.R69.
The influx of L-lysine into apical vesicles from the chicken jejunum occurs through two systems, one with low Michaelis constant (K(m)) and features of system b0,+ and the other with relatively high K(m) for L-lysine and with properties of system y+. In the present study the effect of a lysine-enriched diet (Lys, containing 68 g L-lysine/kg dietary protein, control animals 48 g/kg) on L-lysine uptake through both transport systems was investigated. Results show that 1) lysine enrichment had no effect on either body weight or the efficiency of food utilization. 2) In Lys-fed animals, the mediated L-lysine influx was best fitted to the two-system model with y+ and b0,+ activity. 3) In the presence of an Na+ gradient, total L-lysine uptake is significantly higher in Lys-fed animals than in control birds (about 40% increase). 4) Lys diet increases K(m)b0,+ 6-fold (KSCN gradient) and 12-fold (NaSCN gradient) and maximum velocity (Vmax) by 6- and 20-fold, respectively. The effects of Lys enrichment on the y(+)-like system are only observed on the Vmax and in the presence of a Na+ gradient (30% increase). 5) Na+ is involved in the activation of the transport process in the Lys-fed chickens, but there is no correlation between external Na+ concentration and L-lysine influx. In conclusion, both b(0,+)- and y(+)-like transport systems are upregulated by dietary lysine but with different kinetic profiles; the high-capacity y(+)-like carrier shows a Vmax increase without changes in K(m), whereas the low-capacity b(0,+)-like system shows an increase in Vmax as well as in the K(m).
L-赖氨酸从鸡空肠进入顶端小泡是通过两个系统进行的，一个系统的米氏常数（K(m)）较低，具有b0,+系统的特征，另一个系统对L-赖氨酸的K(m)相对较高，具有y+系统的特性。在本研究中，研究了富含赖氨酸的日粮（赖氨酸，含68 g L-赖氨酸/kg膳食蛋白质，对照动物为48 g/kg）对通过这两种转运系统摄取L-赖氨酸的影响。结果表明：1）赖氨酸富集对体重或食物利用效率均无影响。2）在饲喂赖氨酸的动物中，介导的L-赖氨酸内流最符合具有y+和b0,+活性的双系统模型。3）在存在Na+梯度的情况下，饲喂赖氨酸的动物中L-赖氨酸的总摄取量显著高于对照鸡（增加约40%）。4）赖氨酸日粮使K(m)b0,+分别增加6倍（KSCN梯度）和12倍（NaSCN梯度），最大速度（Vmax）分别增加6倍和20倍。赖氨酸富集对类y(+)-系统的影响仅在Vmax以及存在Na+梯度时观察到（增加30%）。5）Na+参与了饲喂赖氨酸的鸡的转运过程激活，但外部Na+浓度与L-赖氨酸内流之间没有相关性。总之，b(0,+)-和类y(+)-转运系统均受日粮赖氨酸上调，但具有不同的动力学特征；高容量的类y(+)-载体显示Vmax增加而K(m)不变，而低容量的类b(0,+)-系统显示Vmax和K(m)均增加。
