Kinetic properties of the inhibition of juvenile hormone esterase by two trifluoromethylketones and O-ethyl,S-phenyl phosphoramidothioate

Yehia A I Abdel-Aal, Richard M. Roe, Bruce D. Hammock

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Abstract

Some inhibition kinetic properties and in vivo inhibition of the plasma juvenile hormone esterase from the cabbage looper (Trichoplusia ni Hübner) by one phosphoramidothioate and two trifluoromethylketones were examined. O-ethyl,S-phenyl phosphoramidothioate was shown to react irreversibly with the enzyme in a time-dependent manner, and the inhibition reaction can be factored into a reversible step with a dissociation constant, Kd, of 4.55 × 10-5 M followed by a phosphorylation step with a rate constant, k2, of 1.98 min-1. The phosphorylated enzyme did not show spontaneous recovery after 48 hr of dialysis. On the other hand, the two trifluoromethylketones were shown to act as reversible inhibitors, as their inhibited enzyme was regenerated completely after dialysis. However, 1,1,1,-trifluoro-3-thiooctylpropan-2-one, in contrast to 1,1,1-trifluorotetradecan-2-one, showed progressive time-dependent inhibition, and its reaction with the enzyme followed characteristic bimolecular second-order kinetics with a rate constant, ki, of 3.37 × 107 M-1 min-1. The in vivo inhibition data of topically treated larvae at equimolar amounts of the tested compounds indicated rapid penetration, and the stability of the inhibition was higher for the phosphoramidothioate than for the trifluoromethylketones. The relationship of the mechanism of inhibition and the in vivo inhibition of these compounds to the understanding of the interactions between juvenile hormone and juvenile hormone esterase is discussed.

Original languageEnglish (US)
Pages (from-to)232-241
Number of pages10
JournalPesticide Biochemistry and Physiology
Volume21
Issue number2
DOIs
StatePublished - 1984

Fingerprint

juvenile hormone esterase
kinetics
Trichoplusia ni
Kinetics
Dialysis
Enzymes
dialysis
enzymes
Rate constants
reaction inhibition
Juvenile Hormones
Phosphorylation
Brassica
juvenile hormones
Larva
phosphorylation
Plasmas
Recovery
larvae

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Biochemistry
  • Physiology

Cite this

Kinetic properties of the inhibition of juvenile hormone esterase by two trifluoromethylketones and O-ethyl,S-phenyl phosphoramidothioate. / Abdel-Aal, Yehia A I; Roe, Richard M.; Hammock, Bruce D.

In: Pesticide Biochemistry and Physiology, Vol. 21, No. 2, 1984, p. 232-241.

Research output: Contribution to journalArticle

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abstract = "Some inhibition kinetic properties and in vivo inhibition of the plasma juvenile hormone esterase from the cabbage looper (Trichoplusia ni H{\"u}bner) by one phosphoramidothioate and two trifluoromethylketones were examined. O-ethyl,S-phenyl phosphoramidothioate was shown to react irreversibly with the enzyme in a time-dependent manner, and the inhibition reaction can be factored into a reversible step with a dissociation constant, Kd, of 4.55 × 10-5 M followed by a phosphorylation step with a rate constant, k2, of 1.98 min-1. The phosphorylated enzyme did not show spontaneous recovery after 48 hr of dialysis. On the other hand, the two trifluoromethylketones were shown to act as reversible inhibitors, as their inhibited enzyme was regenerated completely after dialysis. However, 1,1,1,-trifluoro-3-thiooctylpropan-2-one, in contrast to 1,1,1-trifluorotetradecan-2-one, showed progressive time-dependent inhibition, and its reaction with the enzyme followed characteristic bimolecular second-order kinetics with a rate constant, ki, of 3.37 × 107 M-1 min-1. The in vivo inhibition data of topically treated larvae at equimolar amounts of the tested compounds indicated rapid penetration, and the stability of the inhibition was higher for the phosphoramidothioate than for the trifluoromethylketones. The relationship of the mechanism of inhibition and the in vivo inhibition of these compounds to the understanding of the interactions between juvenile hormone and juvenile hormone esterase is discussed.",
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