Majetschak M, Laub M, Jennissen H P
Institut für Physiologische Chemie, Universität-GHS-Essen, Germany.
FEBS Lett. 1993 Jan 11;315(3):347-52. doi: 10.1016/0014-5793(93)81192-3.
Ubiquityl-calmodulin synthetase (uCaM-synthetase) activity as detected in reticulocyte lysate and the crude extracts of rabbit tissues [FEBS Lett. 294 (1991) 229-233] has been well characterized as being essentially Ca(2+)-dependent (-Ca2+/+Ca2+ activity ratio: 0.15-0.2). However, during the purification of this enzyme on ubiquitin-Sepharose the Ca(2+)-dependent activity is lost and an essentially Ca(2+)-independent enzyme (-Ca2+/+Ca2+ activity ratio: 1.0-1.5) is obtained which was purified 90-fold (uCaM-Syn F1) to a final specific activity of 0.32 pkat/mg. During the purification procedure a second protein factor (uCaM-Syn F2) was isolated that has no catalytic activity by itself but restores Ca2+ dependence to the uCaM-Syn F1 fraction (-Ca2+/+Ca2+ activity ratio: 0.1) and enhances the catalytic activity in uCaM-Syn F1 in the presence of Ca2+ over 40-fold. It is concluded that several (possibly interdependent) forms of uCaM-synthetase exist which display different substrate specificities for calmodulin.
在网织红细胞裂解物和兔组织粗提物中检测到的遍在蛋白 - 钙调蛋白合成酶（uCaM - 合成酶）活性[《欧洲生物化学学会联合会快报》294 (1991) 229 - 233]已被充分表征为基本上依赖于Ca(2+)（-Ca2+/+Ca2+活性比：0.15 - 0.2）。然而，在利用泛素 - 琼脂糖对该酶进行纯化过程中，Ca(2+)依赖性活性丧失，得到一种基本上不依赖Ca(2+)的酶（-Ca2+/+Ca2+活性比：1.0 - 1.5），该酶纯化了90倍（uCaM - Syn F1），最终比活性为0.32 pkat/mg。在纯化过程中，分离出了第二种蛋白质因子（uCaM - Syn F2），其自身没有催化活性，但能使uCaM - Syn F1组分恢复Ca2+依赖性（-Ca2+/+Ca2+活性比：0.1），并在Ca2+存在下将uCaM - Syn F1中的催化活性提高40多倍。得出的结论是，存在几种（可能相互依赖的）uCaM - 合成酶形式，它们对钙调蛋白表现出不同的底物特异性。
