Majumder G C
Biochem J. 1977 Sep 1;165(3):469-77. doi: 10.1042/bj1650469.
A nuclear protein kinase that shows a high degree of substrate specificity for the phosphorylation of the acidic proteins casein, phosvitin and non-histone chromatin proteins, rather than the basic proteins histones and protamine, was partially purified from lactatingrat mammary gland. The enzyme is associated with the acidic protein fraction of chromatin. Nuclear kinase requires Co(2+) for activity, and other bivalent cations such as Mg(2+) and Mn(2+) can substitute partially for Co(2+). The kinase is further activates (2-3-fold) by various salts, their concentration for maximum stimulation being: NaCl, 150mm; KCl, 200mm; sodium acetate, 300mm. The sedimentation coefficient of the nuclear kinase is 8.9S and its mol.wt. is approx. 300000 by gel-exclusion chromatography. The enzyme is not activated by cyclic AMP or cyclic GMP and is inhibited neither by the regulatory subunit of mammary cyclic AMP-dependent protein kinase nor by the heat-stable protein kinase inhibitor from ox heart. Analysis of (32)P-labelled protein products reveals that the kinase transfers the terminal phosphate of ATP to serine and threonine residues of proteins. The enzyme, however, has specificity for the phosphorylation of threonine in casein and serine in phosvitin. Molecular size and enzymic characteristics of the nuclear protein kinase are clearly different from those of the cytosol enzyme previously characterized.
从泌乳大鼠乳腺中部分纯化出一种核蛋白激酶，该激酶对酸性蛋白酪蛋白、卵黄高磷蛋白和非组蛋白染色质蛋白的磷酸化表现出高度的底物特异性，而对碱性蛋白组蛋白和鱼精蛋白则不然。该酶与染色质的酸性蛋白部分相关。核激酶的活性需要Co(2+)，其他二价阳离子如Mg(2+)和Mn(2+)可部分替代Co(2+)。该激酶可被各种盐进一步激活（2 - 3倍），其最大刺激浓度分别为：NaCl，150mM；KCl，200mM；醋酸钠，300mM。核激酶的沉降系数为8.9S，通过凝胶排阻色谱法测得其分子量约为300000。该酶不受环磷酸腺苷（cAMP）或环磷酸鸟苷（cGMP）激活，也不受乳腺环磷酸腺苷依赖性蛋白激酶的调节亚基或牛心热稳定蛋白激酶抑制剂的抑制。对(32)P标记的蛋白产物分析表明，该激酶将ATP的末端磷酸基团转移至蛋白的丝氨酸和苏氨酸残基上。然而，该酶对酪蛋白中的苏氨酸磷酸化和卵黄高磷蛋白中的丝氨酸磷酸化具有特异性。核蛋白激酶的分子大小和酶学特性与先前鉴定的胞质溶胶酶明显不同。
