Desmosterol, an intermediate in dealkylation of β-sitosterol in the tobacco hornworm

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Desmosterol, an intermediate in dealkylation of β-sitosterol in the tobacco hornworm

Year: 

1967

Source of publication :

Life Sciences

Authors :

Svoboda, James

.

Volume :

Co-Authors: 

Svoboda, J.A., Insect Physiology Laboratory, Entomology Research Division, ARS, Beltsville, MD 20705, United States
Thompson, M.J., Insect Physiology Laboratory, Entomology Research Division, ARS, Beltsville, MD 20705, United States
Robbins, W.E., Insect Physiology Laboratory, Entomology Research Division, ARS, Beltsville, MD 20705, United States

From page: 

395

To page: 

404

(

Total pages: 

10

)

Link :

Desmosterol, an intermediate in dealkylation of β-sitosterol in the tobacco hornworm

Abstract: 

The mechanism of dealkylation of phytosterols such as β-sitosterol to cholesterol in insects is an important and little understood biochemical transformation. This alteration of the sterol side chain provides a means for omnivorous and particularly phytophagous insects to obtain their essential cholesterol from foodstuffs that are either very low or completely lacking in cholesterol but which contain substantial quantities of plant sterols. Dealkylation has been reported or inferred for a number of insects and has definitely been demonstrated to occur in certain species through the use of semidefined diets, radiotracer labeled sterols, and/or gas-liquid chromatographic analysis (1,2,3). In these insects, only the final metabolite of this process, cholesterol or a cholestane derivative, has been identified, and nothing is known of the intermediate reactions. Recent research has greatly enhanced our understanding of the alkylation process that occurs during the biosynthesis of plant sterols (4,5,6). It would be of extreme interest from a comparative biochemical standpoint to determine whether the alkylation and dealkylation processes share certain common intermediates or proceed through common pathways. During a study in our laboratory on the rate of conversion of H3-β-sitosterol to cholesterol in the tobacco hornworm, Manduca sexta (Johannson), an unknown H3-labeled sterol component was detected. The isolation and identification of this sterol as desmosterol (Δ5,24-cholestadien-3β-o1) and proof of its occurrence as an intermediate in the dealkylation process is the topic of this report. © 1967.