Vargas Zapata C L, Trugo N M, Donangelo C M
Laboratório de Bioquímica Nutricional e de Alimentos, Departamento de Bioquímica, Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil.
Biol Trace Elem Res. 2000 Feb;73(2):127-37. doi: 10.1385/bter:73:2:127.
Zinc uptake by syncytiotrophoblast microvillous membrane vesicles (SMMV) from human placentas was characterized and the effects of maternal serum zinc levels at term and of gestational age on kinetic parameters were evaluated. Zinc uptake at pH 7.2 was rapid for the first 2 min, followed by a slower increase, approaching equilibrium after 30 min. Uptake was saturable at a zinc concentration of 30 micromol/L, higher than the upper range of the physiological serum zinc level. Kinetic analysis of uptake at 1 min in SMMV from term placenta showed similar Km values (mean: 6.9+/-0.6 micromol/L) for different levels of maternal serum zinc. However, Vmax was higher (p < 0.05) in SMMV from mothers with serum zinc lower than 7.6 micromol/L compared to those with higher serum zinc levels (35.8+/-1.6 and 26.6+/-1.6 nmol 65Zn/mg protein/min, respectively). Km values were similar in term (>37 wk of gestation) and preterm (20-25 wk of gestation) placentas, whereas Vmax was higher (p < 0.05) in the preterm (34.3+/-1.6 nmol Zn/mg protein/min) compared to term placentas from mothers with serum zinc levels above 7.6 micromol/L. These results suggest that whereas afffinity for zinc was not altered with gestational age or maternal serum zinc levels, zinc-uptake capacity in human placenta is influenced both by gestational age and by low levels of maternal serum zinc in order to ensure an adequate maternal-fetal zinc transfer.
对来自人胎盘的合体滋养层微绒毛膜囊泡（SMMV）摄取锌的特性进行了表征，并评估了足月时母体血清锌水平和胎龄对动力学参数的影响。在pH 7.2条件下，锌的摄取在前2分钟迅速进行，随后增加较慢，30分钟后接近平衡。在锌浓度为30微摩尔/升时摄取达到饱和，该浓度高于生理血清锌水平的上限。对足月胎盘SMMV中1分钟时摄取情况的动力学分析表明，不同母体血清锌水平下的Km值相似（平均值：6.9±0.6微摩尔/升）。然而，与血清锌水平较高的母亲的SMMV相比，血清锌低于7.6微摩尔/升的母亲的SMMV的Vmax更高（p<0.05）（分别为35.8±1.6和26.6±1.6纳摩尔65Zn/毫克蛋白质/分钟）。足月（妊娠>37周）和早产（妊娠20 - 25周）胎盘的Km值相似，而对于血清锌水平高于7.6微摩尔/升的母亲，早产胎盘的Vmax高于足月胎盘（p<0.05）（34.3±1.6纳摩尔锌/毫克蛋白质/分钟）。这些结果表明，尽管胎盘对锌的亲和力不会随胎龄或母体血清锌水平而改变，但为确保母体 - 胎儿之间充足的锌转运，人胎盘摄取锌的能力受胎龄和母体血清锌低水平的影响。
