En-Nya A, Gueant J L, Nexø E, Gerard A, Boukhzer E B, Nicolas J P, Gerard H
Laboratoire d'Histologie-Embryologie II, Faculté de Médecine de Nancy, France.
Int J Dev Biol. 1993 Jun;37(2):353-7.
The binding of 125I-iodinated transcobalamin to a suspension of isolated rabbit germ cells was studied by Scatchard plot. The number of binding sites was evaluated to about 1000 per cell, and its association constant (Kass) in order of 14.6 l/nmole. The distribution to structures related to endocytosis was determined by ultrastructural histomorphometric studies. Both coated and uncoated structures were present regardless of maturation stage. The number of coated vesicles was at its highest in the initial maturation steps, whereas the number of uncoated vesicles was highest in the final maturation steps. The endocytosis of 125I-iodinated transcobalamin by the suspension of germ cells was studied by electron microscope radioautography. The tracer was mostly detected over the plasma membrane, coated vesicles and multivesicular bodies of germ cells. The grains were observed mainly over spermatocytes and round spermatids; 31.6% and 32% of these cells, respectively, were labeled. In contrast the tracer was detected in only 8.11% of elongated spermatids. In conclusion, iodinated transcobalamin is internalized in rabbit germ cells by receptor-mediated endocytosis. This phenomenon was predominant in the early stages of germ cell maturation.
采用Scatchard作图法研究了125I标记的转钴胺素与分离的兔生殖细胞悬液的结合情况。结合位点数量评估为约每个细胞1000个，其缔合常数（Kass）约为14.6 l/nmol。通过超微结构组织形态计量学研究确定了其在与胞吞作用相关结构中的分布。无论成熟阶段如何，均存在有被和无被结构。有被小泡数量在初始成熟步骤中最高，而无被小泡数量在最终成熟步骤中最高。通过电子显微镜放射自显影术研究了生殖细胞悬液对125I标记的转钴胺素的胞吞作用。示踪剂主要在生殖细胞的质膜、有被小泡和多泡体上检测到。颗粒主要在精母细胞和圆形精子细胞上观察到；这些细胞分别有31.6%和32%被标记。相比之下，仅在8.11%的长形精子细胞中检测到示踪剂。总之，碘化转钴胺素通过受体介导的胞吞作用在兔生殖细胞中内化。这种现象在生殖细胞成熟的早期阶段占主导地位。
