Carré I A, Edmunds L N
Department of Anatomical Sciences, State University of New York, Stony Brook 11794.
J Biol Chem. 1992 Feb 5;267(4):2135-7.
Euglena cells grown in diurnal light-dark cycles exhibit circadian variations of their cAMP content, which we believe to be under the control of an endogenous timer because they persist in constant darkness in the absence of any environmental time cue. We think that these cAMP oscillations may play a role in the regulation of some of the numerous cellular activities that are known to display circadian rhythmicities in this organism. The role of cAMP in algal cells is still controversial, however, since the nature of the cAMP "receptor" is unknown. We show that extracts of the achlorophyllous ZC mutant of Euglena gracilis contain two cAMP-binding proteins, which bind cAMP with a high affinity (Kd values of 10 nM and 30 nM) and which can be separated by DEAE-cellulose chromatography. Protein kinase activity was assayed using Kemptide as a substrate. Stimulation of kinase activity by cAMP was observed after partial purification by DEAE-cellulose chromatography. Two peaks of activity were resolved, corresponding to distinct enzymes with different cAMP-analog specificities. Thus, cAMP signaling in plant cells may proceed by the phosphorylation of target proteins by cAMP-dependent kinases, in a manner similar to that of animal cells.
在昼夜明暗循环中生长的眼虫细胞，其环磷酸腺苷（cAMP）含量呈现昼夜节律变化。我们认为这是由一个内源性定时器控制的，因为在没有任何环境时间线索的持续黑暗中，这种变化依然存在。我们认为这些cAMP振荡可能在调节该生物体中众多已知呈现昼夜节律的细胞活动中发挥作用。然而，cAMP在藻类细胞中的作用仍存在争议，因为cAMP“受体”的性质尚不清楚。我们发现，纤细裸藻无叶绿素的ZC突变体提取物含有两种cAMP结合蛋白，它们以高亲和力结合cAMP（解离常数Kd值分别为10 nM和30 nM），并且可以通过DEAE - 纤维素色谱法分离。以肯普肽为底物测定蛋白激酶活性。经DEAE - 纤维素色谱法部分纯化后，观察到cAMP对激酶活性的刺激作用。分辨出两个活性峰，对应于具有不同cAMP类似物特异性的不同酶。因此，植物细胞中的cAMP信号传导可能通过cAMP依赖性激酶对靶蛋白的磷酸化来进行，其方式与动物细胞类似。
