Redox potentials and quinone reductase activity of L-aspartate oxidase from Escherichia coli.
l-Aspartate oxidase (EC 1.4.3.16) is a flavoprotein that catalyzes the first step in the de novobiosynthetic pathway to pyridine nucleotides both under aerobic and under anaerobic conditions. Despite the physiological importance of this biosynthesis particularly in facultative aerobic organisms, such as Escherichia coli, little is known about the electron acceptor of reduced L-aspartate oxidase in the absence of oxygen. In this report, evidence is presented which suggests that in vitro quinones can play such a role. L-Aspartate oxidase binds menadione and 2, 3-dimethoxy-5-methyl-p-benzoquinone with Kd values of 11.5 and 2.4 microM, respectively. A new L-aspartate:quinone oxidoreductase activity is described in the presence and in the absence of phospholipids, and its possible physiological relevance is discussed. Moreover, considering the striking sequence similarity between L-aspartate oxidase and the highly conserved family of succinate-fumarate oxidoreductases, the redox properties of L-aspartate oxidase were investigated in detail. A value of -216 mV was calculated for the midpoint potential of the couple FAD/FADH2 bound to the enzyme. This result perfectly explains why L-aspartate oxidase may be considered as a very particular fumarate reductase unable to use succinate as the electron donor.
Tedeschi
G
G
Istituto di Fisiologia Veterinaria e Biochimica, Università di Milano and Centro Interuniversitario per lo Studio delle Macromolecole Informazionali, 20133 Milano, Italy.
Zetta
L
L
Negri
A
A
Mortarino
M
M
Ceciliani
F
F
Ronchi
S
S
D000594:Amino Acid Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001665:Binding Sites; D004396:Coloring Agents / Q000378:metabolism; D004579:Electron Transport; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D005420:Flavoproteins / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D011485:Protein Binding; D011809:Quinones / Q000378:metabolism; D016415:Sequence Alignment; D013053:Spectrophotometry; D013385:Succinate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D014812:Vitamin K / Q000494:pharmacology
D004396:Coloring Agents; D029968:Escherichia coli Proteins; D005420:Flavoproteins; D008081:Liposomes; D011809:Quinones; D014812:Vitamin K; D013385:Succinate Dehydrogenase; D000594:Amino Acid Oxidoreductases; C031955:L-aspartate oxidase, E coli; D016660:NAD(P)H Dehydrogenase (Quinone)