The Hydrolysis of Steroid Conjugates

Bradlow, H. Leon

doi:10.1007/978-3-642-49793-3_3

Cited by 4 publications

References 172 publications

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In vitro ecdysteroid conjugation by enzymes of Manduca sexta midgut cytosol

Weirich

Thompson

Svoboda

1986

Arch Insect Biochem Physiol

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In incubations with 80,OOOg supernatant of Manduca sexta midgut homogenates, [3H]ecdysone was converted to 3-[3H]epiecdysone and tritiumlabeled highly polar metabolites. CI8 SEP-PAK cartridges were found suitable for the separation and purification of the free ecdysteroids and of the highly polar metabolites. Eighty to ninety percent of the metabolites were hydrolyzed by enzyme mixtures (mainly 0-glucuronidase, sulphatase, and acid phosphatase) from molluscs, even when 0-glucuronidase activity was completely inhibited by D-saccharic acid 1,4lactone, or various human acid phosphatases (free of sulphatase activity). In each experiment, the hydrolysate contained a much higher proportion of 3-epiecydsone than the free (unconjugated) ecdysteroid fraction. [3H]ecdysone was not metabolized in anaerobic incubations of midgut supernatant that had been filtered through Sephadex C-25. Addition of 5 m M ATP and 5 m M Mg2+ restored the conjugate formation in incubations of Sephadex-filtered supernatant. Four ecdysone conjugates and two 3-epiecdysone conjugates were resolved by reversedphase ion-pair high-performance liquid chromatography. It i s concluded that the midgut cytosol contains several ATP:ecdysteriod phosphotransferases. This is the first demonstration of the formation of ecdysteroid phosphoconjugates in a cell-free system.

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In vitro ecdysteroid conjugation by enzymes of Manduca sexta midgut cytosol

Weirich

Thompson

Svoboda

1986

Arch Insect Biochem Physiol

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Techniques for Extraction and Group Separation of Bile Acids

Sjövall

Setchell

1988

The Bile Acids: Chemistry, Physiology, and Metabolism

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Synthesis and metabolism of vertebrate-type steroids by tissues of insects: A critical evaluation

1991

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This review covers the synthesis and the metabolism of vertebrate-type steroids (progesterone, testosterone, estradiol, corticosteroids) by insect tissues and discusses the significance of the reactions for insect physiology. Biosynthesis of vertebrate-type steroids from cholesterol hitherto has been demonstrated in only two insect species, i.e. the water beetle Acilius sulcatus (Coleoptera) and the tobacco hornworm Manduca sexta (Lepidoptera). In Acilius, steroid synthesis is associated with exosecretion (chemical defense). Nothing, however, is known about a physiological role of the C21 steroid conjugate present in ovaries and eggs of Manduca. No synthesis of vertebrate-type steroids was observed in any other insect investigated to date. Most metabolic conversions of steroids by insects concerned oxidoreduction of oxygen groups (hydroxysteroid dehydrogenase activity) and (polar and apolar) conjugate formation. All important enzymatic steps involved in synthesis and catabolism, as known from studies with tissues of vertebrates, were not, or hardly observed. The conclusion is drawn that typical vertebrate-type (C21, C19 and C18) steroids probably do not act as physiologically active substances in insects.

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The Hydrolysis of Steroid Conjugates

Cited by 4 publications

References 172 publications

In vitro ecdysteroid conjugation by enzymes of Manduca sexta midgut cytosol

In vitro ecdysteroid conjugation by enzymes of Manduca sexta midgut cytosol

Techniques for Extraction and Group Separation of Bile Acids

Synthesis and metabolism of vertebrate-type steroids by tissues of insects: A critical evaluation

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