title: Phosphorylation-dependent regulation of amidotransferase during the development of Blastocladiella emersonii.
abstract: 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.
authors.affiliation: Departamento de Bioquímica, Universidade de São Paulo, Brazil.
authors.forename: L C
authors.initials: LC
authors.lastname: Etchebehere
authors.forename: J C
authors.initials: JC
authors.lastname: Maia
mesh_terms: D001754:Blastocladiella / Q000201:enzymology*; D002499:Centrifugation, Density Gradient; D002845:Chromatography; D008411:Chytridiomycota / Q000201:enzymology*; D004789:Enzyme Activation; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D000637:Transaminases / Q000378:metabolism*; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism
chemical_list: D014537:Uridine Diphosphate N-Acetylglucosamine; D000637:Transaminases; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D010749:Phosphoprotein Phosphatases