Cohen P T, Cohen P
Department of Biochemistry, Medical Sciences Institute, University, Dundee, Scotland, U.K.
Biochem J. 1989 Jun 15;260(3):931-4. doi: 10.1042/bj2600931.
Infection of Escherichia coli with phage lambda gt10 resulted in the appearance of a protein phosphatase with activity towards 32P-labelled casein. Activity reached a maximum near the point of cell lysis and declined thereafter. The phosphatase was stimulated 30-fold by Mn2+, while Mg2+ and Ca2+ were much less effective. Activity was unaffected by inhibitors 1 and 2, okadaic acid, calmodulin and trifluoperazine, distinguishing it from the major serine/threonine-specific protein phosphatases of eukaryotic cells. The lambda phosphatase was also capable of dephosphorylating other substrates in the presence of Mn2+, although activity towards 32P-labelled phosphorylase was 10-fold lower, and activity towards phosphorylase kinase and glycogen synthase 25 50-fold lower than with casein. No casein phosphatase activity was present in either uninfected cells, or in E. coli infected with phage lambda gt11. Since lambda gt11 lacks part of the open reading frame (orf) 221, previously shown to encode a protein with sequence similarity to protein phosphatase-1 and protein phosphatase-2A of mammalian cells [Cohen, Collins, Coulson, Berndt & da Cruz e Silva (1988) Gene 69, 131-134], the results indicate that ORF221 is the protein phosphatase detected in cells infected with lambda gt10. Comparison of the sequence of ORF221 with other mammalian protein phosphatases defines three highly conserved regions which are likely to be essential for function. The first of these is deleted in lambda gt11.
用噬菌体λgt10感染大肠杆菌后，出现了一种对32P标记的酪蛋白具有活性的蛋白磷酸酶。该活性在细胞裂解点附近达到最大值，之后下降。该磷酸酶受到Mn2+的30倍刺激，而Mg2+和Ca2+的刺激效果则差得多。其活性不受抑制剂1、抑制剂2、冈田酸、钙调蛋白和三氟拉嗪的影响，这使其与真核细胞中的主要丝氨酸/苏氨酸特异性蛋白磷酸酶区分开来。在存在Mn2+的情况下，λ磷酸酶也能够使其他底物去磷酸化，尽管其对32P标记的磷酸化酶的活性低10倍，对磷酸化酶激酶和糖原合酶的活性比对酪蛋白低25至50倍。在未感染的细胞或用噬菌体λgt11感染的大肠杆菌中均不存在酪蛋白磷酸酶活性。由于λgt11缺少开放阅读框（orf）221的一部分，先前已证明该开放阅读框编码的蛋白质与哺乳动物细胞的蛋白磷酸酶-1和蛋白磷酸酶-2A具有序列相似性[科恩、柯林斯、库尔森、伯恩特和达·克鲁兹·达·席尔瓦（1988年），《基因》69卷，第131 - 134页]，结果表明ORF221就是在被λgt10感染的细胞中检测到的蛋白磷酸酶。将ORF221的序列与其他哺乳动物蛋白磷酸酶进行比较，确定了三个高度保守的区域，这些区域可能对其功能至关重要。其中第一个区域在λgt11中缺失。
