Wheeler T T, Broadhurst M K, Rajan G H, Wilkins R J
Dairy Science Group, AgResearch, Ruakura Research Centre, Hamilton, New Zealand.
J Dairy Sci. 1997 Sep;80(9):2011-9. doi: 10.3168/jds.S0022-0302(97)76145-9.
The mechanisms that control the synthesis of milk protein are not fully understood and could well involve undiscovered proteins within the mammary gland. A search for such proteins in high salt extracts of nuclei that had been isolated from bovine mammary tissues was undertaken using two-dimensional electrophoresis on large format gels. The sensitivity of the procedure was sufficient to detect the transcription factors Sp1 and NF-1 by Coomassie blue stain; over 300 proteins were routinely detected. Analysis of mammary tissue taken from 5 nonlactating cows in midpregnancy, 5 cows in late lactation, and 4 cows in early involution revealed five proteins where relative abundance was altered with stage of lactation or reproductive cycle. Four of these proteins were identified by Western blotting or amino acid sequencing as lactoferrin, annexin II, vimentin, and heavy-chain immunoglobulin. Analysis of proteins after further enrichment of the extracts by heparin-Sepharose affinity chromatography revealed an additional protein that was substantially more abundant in samples from lactating cows. This 90-kDa protein did not react with anti-Stat5 antibodies. Conceivably, one or more of these six proteins could play a role in the lactational function of the bovine mammary gland.
控制乳蛋白合成的机制尚未完全明了，很可能涉及乳腺内未被发现的蛋白质。利用大型凝胶二维电泳技术，对从牛乳腺组织中分离出的细胞核高盐提取物中的此类蛋白质进行了搜索。该方法的灵敏度足以通过考马斯亮蓝染色检测转录因子Sp1和NF-1；常规检测到300多种蛋白质。对取自5头妊娠中期非泌乳奶牛、5头泌乳后期奶牛和4头 involution早期奶牛的乳腺组织进行分析，发现有5种蛋白质的相对丰度随泌乳阶段或生殖周期而变化。通过蛋白质印迹法或氨基酸测序鉴定出其中4种蛋白质为乳铁蛋白、膜联蛋白II、波形蛋白和重链免疫球蛋白。通过肝素-琼脂糖亲和色谱进一步富集提取物后对蛋白质进行分析，发现了一种在泌乳奶牛样本中含量显著更高的额外蛋白质。这种90 kDa的蛋白质不与抗Stat5抗体反应。可以想象，这六种蛋白质中的一种或多种可能在牛乳腺的泌乳功能中发挥作用。
