Sanchez L, Lujan L, Oria R, Castillo H, Perez D, Ena J M, Calvo M
Facultad de Veterinaria, Zaragoza, Spain.
J Dairy Sci. 1992 May;75(5):1257-62. doi: 10.3168/jds.S0022-0302(92)77875-8.
Two iron-binding proteins, lactoferrin and transferrin, are present in ruminant milk. Lactoferrin commonly has been assumed to be a product of mammary synthesis, but the origin of milk transferrin has not been elucidated. The objective of this experiment was to study the synthesis and distribution of these two proteins in the mammary gland of sheep. Explants from lactating mammary gland of sheep have been cultured in the presence of [3H]leucine to determine rates of synthesis of lactoferrin and transferrin. After incubation, [3H]lactoferrin was found, but labeled transferrin was not. The capacity of the mammary gland to synthesize lactoferrin decreased markedly in the first 24 h of lactation. Immunohistochemical techniques were utilized to identify the locations of lactoferrin and transferrin in the mammary gland. Transferrin was found in the colostrum contained in the alveolar lumen, in the cytoplasm of the secretory cells, and in the connective tissue between the mammary acini. High concentration of transferrin was found in the basal membrane of the secretory alveolar cells, mainly in those near capillary vessels. Lactoferrin was found in the colostrum and in the cytoplasm of secretory cells with a more homogeneous distribution than transferrin. The connective tissue stained negative for lactoferrin. These results suggest that, although lactoferrin is synthesized by mammary gland of the sheep, transferrin comes from blood serum, probably by a receptor-mediated mechanism of transcytosis.
反刍动物乳汁中存在两种铁结合蛋白，即乳铁蛋白和转铁蛋白。通常认为乳铁蛋白是乳腺合成的产物，但乳汁中转铁蛋白的来源尚未阐明。本实验的目的是研究这两种蛋白在绵羊乳腺中的合成及分布情况。将绵羊泌乳期乳腺的外植体在[3H]亮氨酸存在的条件下进行培养，以测定乳铁蛋白和转铁蛋白的合成速率。培养后，发现了[3H]乳铁蛋白，但未发现标记的转铁蛋白。在泌乳的最初24小时内，乳腺合成乳铁蛋白的能力显著下降。利用免疫组织化学技术确定乳铁蛋白和转铁蛋白在乳腺中的位置。在腺泡腔中的初乳、分泌细胞的细胞质以及乳腺腺泡之间的结缔组织中发现了转铁蛋白。在分泌性腺泡细胞的基底膜中发现了高浓度的转铁蛋白，主要存在于靠近毛细血管的细胞中。在初乳和分泌细胞的细胞质中发现了乳铁蛋白，其分布比转铁蛋白更均匀。结缔组织对乳铁蛋白染色呈阴性。这些结果表明，虽然乳铁蛋白是由绵羊乳腺合成的，但转铁蛋白可能来自血清，可能是通过受体介导的转胞吞作用机制。
