Etchebehere L C, Maia J C
Departamento de Bioquímica, Universidade de São Paulo, Brazil.
Arch Biochem Biophys. 1989 Aug 1;272(2):301-10. doi: 10.1016/0003-9861(89)90223-3.
The enzyme amidotransferase [2-amino-2-deoxy-D-glucose-6-phosphate ketol isomerase (amino-transferring); EC 2.6.1.16] catalyzes the first step in the hexosamine biosynthetic pathway. In Blastocladiella emersonii the sensitivity of the enzyme to the inhibitor uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc) is developmentally regulated. The inhibitable form of amidotransferase activity present in the zoospore is converted to a noninhibitable form during germination. The latter form is present throughout the growth phase and sensitivity to UDP-GlcNAc gradually returns to the zoospore level during sporulation [C.P. Selitrennikoff, N.E. Dalley, and D.R. Sonneborn (1980) Proc. Natl. Acad. Sci. USA 77, 5998-6002]. The following evidence suggests that a phosphorylation/dephosphorylation mechanism underlies this interconversion: (i) Both the vegetative and zoospore enzymes have the same molecular weight of 140,000, but the vegetative enzyme elutes significantly earlier on a DEAE-cellulose column than does the zoospore enzyme. (ii) The increased sensitivity to UDP-GlcNAc occurring in vivo and in vitro correlates with increased phosphorylation of a polypeptide of apparent Mr 76,000. This component copurifies with amidotransferase activity through ion-exchange chromatography and sucrose density gradient centrifugation. (iii) Desensitization and concurrent dephosphorylation of sensitive amidotransferase can be observed in vitro after treatment with a partially purified magnesium-dependent phosphoprotein phosphatase from zoospores.
酰胺转移酶[2-氨基-2-脱氧-D-葡萄糖-6-磷酸酮醇异构酶（氨基转移）；EC 2.6.1.16]催化己糖胺生物合成途径的第一步。在艾美球虫中，该酶对抑制剂尿苷-5'-二磷酸-N-乙酰葡糖胺（UDP-GlcNAc）的敏感性受到发育调控。游动孢子中存在的可被抑制的酰胺转移酶活性形式在萌发过程中会转变为不可被抑制的形式。后一种形式在整个生长阶段都存在，并且在孢子形成期间对UDP-GlcNAc的敏感性逐渐恢复到游动孢子水平[C.P. 塞利特伦尼科夫、N.E. 达利和D.R. 索恩伯恩（1980年）《美国国家科学院院刊》77，5998 - 6002]。以下证据表明这种相互转化的基础是磷酸化/去磷酸化机制：（i）营养体和游动孢子中的酶分子量均为140,000，但营养体酶在DEAE - 纤维素柱上的洗脱时间明显早于游动孢子酶。（ii）体内和体外对UDP-GlcNAc敏感性的增加与表观分子量为76,000的一种多肽磷酸化的增加相关。该组分通过离子交换色谱和蔗糖密度梯度离心与酰胺转移酶活性共纯化。（iii）用来自游动孢子的部分纯化的依赖镁的磷蛋白磷酸酶处理后，在体外可观察到敏感酰胺转移酶的脱敏和同时发生的去磷酸化。
