Miller J G, Schultz G A
J Exp Zool. 1983 Dec;228(3):511-25. doi: 10.1002/jez.1402280311.
The kinetics, specificity, time dependency, Na+ dependency, and exchange behavior of the uptake of methionine, as a model for the uptake of the neutral amino acids, was investigated in rabbit eggs, morulae, and 6-day blastocysts. Uptake by the blastocyst was physically resolved into components representing uptake into the cellular and cavity compartments. The kinetic data for all material, except the cellular compartment of the blastocyst, could be described mathematically by the parallel activity of a saturable and a linear transport system. The Km decreased from 91 microM in the unfertilized egg to 38 microM in the fertilized egg to 13 microM in the 69-hr morula. The Km of uptake into blastocysts was 131 microM. The Vmax of uptake into the whole blastocyst was calculated to be about 5000 times that of uptake into the egg. Competition of methionine uptake by other amino acids indicated that the egg had somewhat more "L-like" transport specificity than subsequent developmental stages, while the system(s) in the blastocyst were reactive with most neutral amino acids. Uptake into the egg, 69-hr morula, and the cellular compartment of the blastocyst reached a steady state with time, in contrast to uptake into the 76-hr morula and the cavity compartment of the blastocyst. Compatible with this, was the observation that eggs and 69-hr morula, but not blastocysts, exhibited considerable efflux into amino acid-containing media. The cavity compartment of the blastocyst may, however, act as a reservoir of amino acids for the cellular compartment. The Na+ dependency of transport was unchanged throughout the developmental period studied in this investigation.
以蛋氨酸作为中性氨基酸摄取的模型，研究了兔卵、桑椹胚和6日龄囊胚中蛋氨酸摄取的动力学、特异性、时间依赖性、钠离子依赖性及交换行为。囊胚的摄取在物理上可分解为代表摄取到细胞和腔室部分的组分。除囊胚的细胞部分外，所有物质的动力学数据都可用一个可饱和转运系统和一个线性转运系统的平行活性进行数学描述。米氏常数（Km）从未受精卵中的91微摩尔降至受精卵中的38微摩尔，再降至69小时桑椹胚中的13微摩尔。囊胚摄取的Km为131微摩尔。整个囊胚摄取的最大反应速度（Vmax）经计算约为卵摄取的5000倍。其他氨基酸对蛋氨酸摄取的竞争表明，卵的“L型”转运特异性比随后的发育阶段略高，而囊胚中的转运系统对大多数中性氨基酸有反应。与卵、69小时桑椹胚及囊胚的细胞部分摄取随时间达到稳态不同，76小时桑椹胚及囊胚的腔室部分摄取并非如此。与此相符的是，观察到卵和69小时桑椹胚，但不是囊胚，在含氨基酸培养基中表现出大量外流。然而，囊胚的腔室部分可能作为细胞部分氨基酸的储存库。在本研究中所研究的整个发育时期，转运的钠离子依赖性没有变化。
