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Possible role for covalent modification in the reversible activation of ecdysone 20‐monooxygenase activity
Author(s) -
Hoggard Nigel,
Fisher Michael J.,
Rees Huw H.
Publication year - 1989
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.940100307
Subject(s) - monooxygenase , phosphatase , biochemistry , phosphoprotein , protein kinase a , biology , cytosol , phosphorylation , ecdysone , calmodulin , kinase , enzyme , cytochrome p450 , hormone
Evidence is presented for the reversible activation‐inactivation of the microsomal ecdysone 20‐monooxygenase from fat body of the cotton leafworm, Spodoptera littoralis , in a manner commensurate with reversible changes in its phosphorylation state. The activity of the monooxygenase was higher following preincubation with fluoride (an inhibitor of phosphoprotein phosphatases) than in its absence. Preincubation with alkaline phosphatase or with cAMP‐dependent protein kinase resulted in appreciable diminution or enhancement, respectively, in monooxygenase activity. Activation of ecdysone 20‐monooxygenase activity could also be effected by incubation with a cytosolic fraction in the presence of cAMP, ATP, and fluoride; this activation was prevented by a cAMP‐dependent protein kinase inhibitor. Similarly, inactivation of the monooxygenase was achieved by preincubation with cytosol, the effect being enhanced by Ca 2+ ‐calmodulin or by Mg 2+ ions. The combined results provide indirect evidence that the microsomal ecdysone 20‐monooxygenase exists in an active phosphorylated form and an inactive dephosphorylated form, interconvertible by a cAMP‐dependent protein kinase and a phosphoprotein phosphatase.