Mechanistic analysis of wheat chlorophyllase

Kiani A.J. Arkus, Edgar B Cahoon, Joseph M. Jez

Research output: Contribution to journalArticle

53 Citations (Scopus)

Abstract

Chlorophyllase catalyzes the initial step in the degradation of chlorophyll and plays a key role in leaf senescence and fruit ripening. Here, we report the cloning of chlorophyllase from Triticum aestivum (wheat) and provide a detailed mechanistic analysis of the enzyme. Purification of recombinant chlorophyllase from an Escherichia coli expression system indicates that the enzyme functions as a dimeric protein. Wheat chlorophyllase hydrolyzed the phytol moiety from chlorophyll (kcat = 566 min-1; Km = 63 μM) and was active over a broad temperature range (10-75 °C). In addition, the enzyme displays carboxylesterase activity toward p-nitrophenyl (PNP)-butyrate, PNP-decanoate, and PNP-palmitate. The pH-dependence of the reaction showed the involvement of an active site residue with a pKa of ∼6.5 for both kcat and kcat/Km with chlorophyll, PNP-butyrate, and PNP-decanoate. Using these substrates, solvent kinetic isotope effects ranging from 1.5 to 1.9 and from 1.4 to 1.9 on kcat and kcat/Km, respectively, were observed. Proton inventory experiments suggest the transfer of a single proton in the rate-limiting step. Our analysis of wheat chlorophyllase indicates that the enzyme uses a charge-relay mechanism similar to other carboxylesterases for catalysis. Understanding the activity and mechanism of chlorophyllase provides insight on the biological and chemical control of senescence in plants and lays the groundwork for biotechnological improvement of this enzyme.

Original languageEnglish (US)
Pages (from-to)146-155
Number of pages10
JournalArchives of Biochemistry and Biophysics
Volume438
Issue number2
DOIs
StatePublished - Jun 15 2005

Fingerprint

chlorophyllase
Triticum
Chlorophyll
Decanoates
Enzymes
Protons
Phytol
Carboxylic Ester Hydrolases
Carboxylesterase
Palmitates
Cloning
Fruits
Catalysis
Isotopes
Escherichia coli
Purification
Organism Cloning
Fruit
Catalytic Domain
Degradation

Keywords

  • Chlorophyll
  • Chlorophyllase
  • Hydrolase
  • Plant senescence
  • Reaction mechanism
  • Triticum aestivum

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

Cite this

Mechanistic analysis of wheat chlorophyllase. / Arkus, Kiani A.J.; Cahoon, Edgar B; Jez, Joseph M.

In: Archives of Biochemistry and Biophysics, Vol. 438, No. 2, 15.06.2005, p. 146-155.

Research output: Contribution to journalArticle

Arkus, Kiani A.J. ; Cahoon, Edgar B ; Jez, Joseph M. / Mechanistic analysis of wheat chlorophyllase. In: Archives of Biochemistry and Biophysics. 2005 ; Vol. 438, No. 2. pp. 146-155.
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