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Absence of phytosterol dealkylation and identification of the major ecdysteroid as makisterone A in Dysdercus fasciatus (Heteroptera, Pyrrhocoridae)
Author(s) -
Gibson J. M.,
Majumder M. S. I.,
Mendis A. H. W.,
Rees H. H.
Publication year - 1983
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.940010111
Subject(s) - ecdysteroid , phytosterol , biology , ecdysone , stigmasterol , heteroptera , instar , campesterol , radioimmunoassay , pentatomidae , sterol , alkylation , botany , biochemistry , chromatography , endocrinology , larva , cholesterol , chemistry , catalysis , genetics
The absence of phytosterol dealkylation in the cotton stainer bug, Dysdercus fasciatus , has been established and the major ecdysteroid in the fifth‐stage larvae identified. The demonstration that the free and esterified sterols in D fasciatus consisted of 95–96% sitosterol and 4–5% campesterol, a similar composition to the cottonseed diet, together with the lack of conversion of [ 14 C]sitosterol into cholesterol, establishes that phytosterol dealkylation does not occur in this insect species. The ecdysteroid titer determined by radioimmunoassay in the fifth instar of D fasciatus shows a distinct peak at day 6, the instar lasting for 7 days. Makisterone A was purified by HPLC from insects at a time of high ecdysteroid titer and identified as a major component by both fast atom bombardment and electron impact mass spectrometry. Gas‐liquid chromatography/mass spectrometry (selected ion monitoring) confirmed the occurrence of makisterone A and revealed the presence of two unidentified compounds. One of these occurs in a similar amount to makisterone A and may be 26‐hydroxymakisterone A, whereas only a minute amount of the other compound, which may be 20‐deoxymakisterone A, was present; further identification of the latter compounds is necessary. C 27 ecdysteroids (eg, ecdysone and 20‐hydroxyecdysone) and C 29 ecdysteroids (eg, podecdysone A) were undetectable. The specificity of the enzymes of ecdysteroid biosynthesis is discussed.