Tokuda M, Khanna N C, Waisman D M
Department of Medical Biochemistry and Cell Regulation Group, University of Calgary, Alberta, Canada.
Biochem J. 1987 Jun 1;244(2):401-8. doi: 10.1042/bj2440401.
A Ca2+-binding protein named CAB-27 was purified from bovine brain 100,000 g supernatant. The protein has a molecular mass of 27,000 Da as determined by SDS/polyacrylamide-gel electrophoresis and 35,500 Da by sedimentation-coefficient and Stokes-radius analysis. The protein contains about 26% Glx and Asx and 13% basic residues. The acidic nature of the molecule is confirmed by its pI of 4.80. In the presence of 3 mM-MgCl2 and 150 mM-KCl, CAB-27 binds 2.0 mol of Ca2+/mol of protein, with an apparent Kd of 0.2 microM. Ca2+-binding is unaffected by prior incubation of the protein at 80 degrees C for 2 min. Brain contains about 130 mg of CAB-27/kg. Immunoblotting identified CAB-27 in several bovine tissues; it appears to be particularly rich in brain and kidney. In addition, CAB-27 is identified as an inhibitor of bovine pancreas phospholipase A2 in vitro. The inhibitory activity of CAB-27 was 20-fold less potent than lipocortin. On the basis of the Ca2+-binding properties, intracellular concentration and tissue distribution of this protein, we suggest that CAB-27 may be an important intracellular Ca2+ receptor.
一种名为CAB - 27的钙结合蛋白是从牛脑100,000 g上清液中纯化得到的。通过SDS/聚丙烯酰胺凝胶电泳测定，该蛋白的分子量为27,000 Da，而通过沉降系数和斯托克斯半径分析，其分子量为35,500 Da。该蛋白含有约26%的谷氨酸和天冬氨酸以及13%的碱性残基。其4.80的等电点证实了该分子的酸性性质。在存在3 mM - MgCl₂和150 mM - KCl的情况下，CAB - 27以每摩尔蛋白结合2.0摩尔Ca²⁺，表观解离常数Kd为0.2 μM。预先将该蛋白在80℃孵育2分钟对Ca²⁺结合没有影响。脑中CAB - 27的含量约为每千克130毫克。免疫印迹法在几种牛组织中鉴定出了CAB - 27；它在脑和肾中似乎特别丰富。此外，CAB - 27在体外被鉴定为牛胰腺磷脂酶A₂的抑制剂。CAB - 27的抑制活性比脂皮质素低20倍。基于该蛋白的Ca²⁺结合特性、细胞内浓度和组织分布，我们认为CAB - 27可能是一种重要的细胞内Ca²⁺受体。
