Kinetics and inhibition of nicotinamidase from mycobacterium tuberculosis

Derrick R. Seiner, Subray Hegde, John S. Blanchard

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Nicotinamidase/pyrazinamidase (PncA) is involved in the NAD+ salvage pathway of Mycobacterium tuberculosis and other bacteria. In addition to hydrolyzing nicotinamide into nicotinic acid, PncA also hydrolyzes the prodrug pyrazinamide to generate the active form of the drug, pyrazinoic acid, which is an essential component of the multidrug treatment of TB. A coupled enzymatic activity assay has been developed for PncA that allows for the spectroscopic observation of enzyme activity. The enzyme activity was essentially pH-independent under the conditions tested; however, the measurement of the pH dependence of iodoacetamide alkylation revealed a pK value of 6.6 for the active site cysteine. Solvent deuterium kinetic isotope effects revealed an inverse value for kcat of 0.64, reconfirming the involvement of a thiol group in the mechanism. A mechanism is proposed for PncA catalysis that is similar to the mechanisms proposed for members of the nitrilase superfamily, in which nucleophilic attack by the active site cysteine generates a tetrahedral intermediate that collapses with the loss of ammonia and subsequent hydrolysis of the thioester bond by water completes the cycle. An inhibitor screen identified the competitive inhibitor 3-pyridine carboxaldehyde with a K i of 290 nM. Additionally, pyrazinecarbonitrile was found to be an irreversible inactivator of PncA, with a kinact/KI of 975 M-1 s-1.

Original languageEnglish (US)
Pages (from-to)9613-9619
Number of pages7
JournalBiochemistry
Volume49
Issue number44
DOIs
StatePublished - Nov 9 2010

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Nicotinamidase
Enzyme activity
nitrilase
Mycobacterium tuberculosis
Cysteine
Catalytic Domain
Water Cycle
Iodoacetamide
Pyrazinamide
Salvaging
Kinetics
Niacinamide
Deuterium
Niacin
Alkylation
Prodrugs
Enzyme Assays
Enzymes
Catalysis
Ammonia

ASJC Scopus subject areas

  • Biochemistry

Cite this

Kinetics and inhibition of nicotinamidase from mycobacterium tuberculosis. / Seiner, Derrick R.; Hegde, Subray; Blanchard, John S.

In: Biochemistry, Vol. 49, No. 44, 09.11.2010, p. 9613-9619.

Research output: Contribution to journalArticle

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