Hoshino A, Hisayasu S, Shimada T
Department of Biochemistry and Molecular Biology, Nippon Medical School, Tokyo, Japan.
Comp Biochem Physiol B Biochem Mol Biol. 1996 Mar;113(3):491-7. doi: 10.1016/0305-0491(95)02068-3.
Rat milk and digestive juices contain transferrin but not lactoferrin, which is a major iron-binding protein in these secretions of human and mouse. To compare the structure of rat transferrin to that of transferrins and lactoferrins in other species, we isolated a cDNA clone containing the entire coding region of transferrin from rat liver and determined its sequence. The amino-acid sequence of rat transferrin had 69.8% identity with that of human transferrin and 48.8% identity with that of human lactoferrin. Rat transferrin, like other transferrins, had the potential N-linked glycosylation site only in the C-terminal domain, although lactoferrins characterized so far contained the glycosylation sites in both the N- and C-terminal domains. Southern and Northern analyses showed that there was the gene specifically hybridized with the mouse lactoferrin cDNA in rat genomic DNA, but only the transferrin mRNA was detected in mammary gland, submaxillary gland and pancreas of rat. These results suggest that the rat lactoferrin gene is silent in the mammary gland, and transferrin can serve as a functional substitute for lactoferrin in rat.
大鼠的乳汁和消化液中含有转铁蛋白，但不含乳铁蛋白，而乳铁蛋白是人和小鼠这些分泌物中的主要铁结合蛋白。为了比较大鼠转铁蛋白与其他物种中转铁蛋白和乳铁蛋白的结构，我们从大鼠肝脏中分离出一个包含转铁蛋白完整编码区的cDNA克隆并确定了其序列。大鼠转铁蛋白的氨基酸序列与人类转铁蛋白的氨基酸序列有69.8%的同源性，与人类乳铁蛋白的氨基酸序列有48.8%的同源性。大鼠转铁蛋白与其他转铁蛋白一样，仅在C末端结构域有潜在的N-连接糖基化位点，而迄今为止所鉴定的乳铁蛋白在N末端和C末端结构域均含有糖基化位点。Southern和Northern分析表明，在大鼠基因组DNA中存在与小鼠乳铁蛋白cDNA特异性杂交的基因，但在大鼠的乳腺、颌下腺和胰腺中仅检测到转铁蛋白mRNA。这些结果表明，大鼠乳铁蛋白基因在乳腺中是沉默的，转铁蛋白可以在大鼠中作为乳铁蛋白的功能替代物。
