title: On the biosynthesis of free and covalently bound PQQ. Glutamic acid decarboxylase from Escherichia coli is a pyridoxo-quinoprotein.
abstract: Analysis of glutamic acid decarboxylase (GDC) (EC 4.1.1.15) from Escherichia coli ATCC 11246 revealed the presence of six pyridoxal phosphates (PLPs) as well as six covalently bound pyrroloquinoline quinones (PQQs) per hexameric enzyme molecule. This is the second example of a pyridoxo-quinoprotein, suggesting that other atypical pyridoxoproteins (PLP-containing enzymes) have similar cofactor composition. Since the organism did not produce free PQQ and its quinoprotein glucose dehydrogenase was present in the apo form, free PQQ is not used in the assemblage of GDC. Most probably, biosynthesis of covalently bound cofactor occurs in situ via a route which is different from that of free PQQ. Thus, organisms previously believed to be unable to synthesize (free) PQQ could in fact be able to produce quinoproteins with covalently bound cofactor. Implications for the role of PQQ in eukaryotic cells are discussed.
authors.affiliation: Department of Microbiology and Enzymology, Delft University of Technology, The Netherlands.
authors.forename: R A
authors.initials: RA
authors.lastname: van der Meer
authors.forename: B W
authors.initials: BW
authors.lastname: Groen
authors.forename: J A
authors.initials: JA
authors.lastname: Duine
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003067:Coenzymes; D004926:Escherichia coli / Q000201:enzymology*; D005968:Glutamate Decarboxylase / Q000032:analysis*; D046911:Macromolecular Substances; D045542:PQQ Cofactor; D011732:Pyridoxal Phosphate / Q000032:analysis; D015363:Quinolones / Q000032:analysis / Q000378:metabolism*
chemical_list: D003067:Coenzymes; D046911:Macromolecular Substances; D015363:Quinolones; D011732:Pyridoxal Phosphate; D045542:PQQ Cofactor; D005968:Glutamate Decarboxylase