Modification of pyruvate-phosphate dikinase with pyridoxal 5'-phosphate: evidence for a catalytically critical lysine residue

Pyruvate, phosphate dikinase from Bacteroides symbiosus is strongly inhibited by low concentrations of pyridoxal 5'-phosphate. The inactivation follows pseudo-first-order kinetics over an inhibitor concentration range of 0.1-2 mM. The inactivation is highly specific since pyridoxine and pyridox...

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Bibliographic Details
Published in:Biochemistry (Easton) 1983-05, Vol.22 (10), p.2518-2523
Main Authors: Phillips, Nelson F. B, Goss, Neil H, Wood, Harland G
Format: Article
Language:English
Subjects:
Bacteroides - enzymology
Bacteroides symbiosus
Kinetics
Lysine
Phosphorus Radioisotopes
Phosphotransferases - metabolism
Protein Binding
pyridoxal 5'-phosphate
Pyridoxal Phosphate - pharmacology
pyruvate, orthophosphate dikinase
Pyruvate, Orthophosphate Dikinase - isolation & purification
Pyruvate, Orthophosphate Dikinase - metabolism
Spectrophotometry, Ultraviolet
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Summary:Pyruvate, phosphate dikinase from Bacteroides symbiosus is strongly inhibited by low concentrations of pyridoxal 5'-phosphate. The inactivation follows pseudo-first-order kinetics over an inhibitor concentration range of 0.1-2 mM. The inactivation is highly specific since pyridoxine and pyridoxamine 5'-phosphate, analogues of pyridoxal 5'-phosphate, which lack an aldehyde group, caused little or no inhibition even at high concentrations. The unreduced dikinase-pyridoxal 5'-phosphate complex displays an absorption maxima near 420 nm, typical for Schiff base formation. Following reduction of the Schiff base with sodium borohydride, N6-pyridoxyllysine was identified in the acid hydrolysate. When the enzyme was incubated in the presence of pyridoxal 5'-phosphate and reducing agent, the ATP/AMP, Pi/PPi, and pyruvate/phosphoenolpyruvate isotopic exchange reactions were inhibited to approximately the same extent, suggesting that the modification of the lysyl moiety causes changes in the enzyme that affect the reactivity of the pivotal histidyl residue. Phosphorylation of the histidyl group appears to prevent the inhibitor from attacking the lysine residue. On the other hand, addition of pyridoxal 5'-phosphate to the pyrophosphorylated enzyme promotes release of the pyrophosphate and yields the free enzyme which is subject to inhibition.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00279a032