Tamura M, Oku T, Hosoya N
J Nutr Sci Vitaminol (Tokyo). 1982 Oct;28(5):533-41. doi: 10.3177/jnsv.28.533.
The Ca2+-binding properties and amino acid compositions of two calcium-binding proteins (mCaBP-3 and mCaBP-4) purified from bovine milk were studied. mCaBP-3 was identified as a Ca2+-bound type and mCaBP-4 as a Ca2+-free type by means of ion-exchange chromatography on a DEAE-Sephadex A-25 column. In polyacrylamide gel disc electrophoresis, both mCaBP-3 and mCaBP-4 had the same mobility of Rf = 0.73 and the addition of 5 mM CaCl2 to the electrode buffer decreased the mobility from Rf = 0.73 to Rf = 0.49. mCaBP-3 and mCaBP-4 consisted of 120 and 122 amino acid residues, respectively. The molecular weights were 13,758 and 13,967, respectively. The amino acid compositions of the two milk CaBPs very closely resembled each other. Both milk CaBPs were rich in aspartic acid, glutamic acid, leucine and lysine, but did not contain trimethylated lysine and amino sugar. An interesting feature is that each milk CaBP contained eight cysteine sulfone and three tryptophan residues per molecule. From these results, it is suggested that mCaBP-3 and mCaBP-4 are identical protein and that mCaBP-3 is formed from mCaBP-4 by means of a conformational change by binding of Ca2+. Thus, mCaBP-3 is a holoprotein and mCaBP-4 is an apoprotein. Furthermore, it is suggested that milk CaBP is different from calmodulin, troponin C and vitamin D-dependent calcium-binding protein.
对从牛乳中纯化得到的两种钙结合蛋白（mCaBP - 3和mCaBP - 4）的钙离子结合特性和氨基酸组成进行了研究。通过在DEAE - Sephadex A - 25柱上进行离子交换色谱法，鉴定出mCaBP - 3为钙离子结合型，mCaBP - 4为无钙离子型。在聚丙烯酰胺凝胶圆盘电泳中，mCaBP - 3和mCaBP - 4的迁移率相同，Rf = 0.73，向电极缓冲液中添加5 mM氯化钙后，迁移率从Rf = 0.73降至Rf = 0.49。mCaBP - 3和mCaBP - 4分别由120和122个氨基酸残基组成。分子量分别为13,758和13,967。两种乳钙结合蛋白的氨基酸组成非常相似。两种乳钙结合蛋白都富含天冬氨酸、谷氨酸、亮氨酸和赖氨酸，但不含三甲基赖氨酸和氨基糖。一个有趣的特征是，每种乳钙结合蛋白每分子含有八个半胱氨酸砜和三个色氨酸残基。从这些结果表明，mCaBP - 3和mCaBP - 4是相同的蛋白质，并且mCaBP - 3是通过钙离子结合引起的构象变化由mCaBP - 4形成的。因此，mCaBP - 3是全蛋白，mCaBP - 4是脱辅基蛋白。此外，表明乳钙结合蛋白与钙调蛋白、肌钙蛋白C和维生素D依赖性钙结合蛋白不同。
