Ecdysteroids ponasterone

Table 3 Imaginal disc bioassays, giving the concentration of ecdysteroid required for 50% evagination (EC50) and the IC50 or Kd value determined from a competion assay for specifically bound [3H]ponasterone A.

Figure 9 Generalised scheme for an ecdysteroid-regulated gene switch system RXR = retinoid X receptor, EcR = ecdysteroid receptor, EcRE = ecdysteroid response element, MuA = muristerone A, PoA = ponasterone A.

Table 6 Kd values for a range of ecdysteroids and two bisacylhydrazines in cell-free extracts of Bn cells. Competition assays were performed with [3H]ponasterone A (0.2 nM), followed by charcoal assay, to determine IC50 values, which were then converted to Kd values. Data taken from [143],...

Ecdysteroids All ecdysteroids used in this work were a kind gift of Prof. Dr. Jan Koolmann, University of Marburg. They were ecdysone, 20-hydroxyecdysone, makisterone and muristerone for the growth experiments, as well as radiolabeled ponasterone A for the binding assay. Preparation of stock solutions, sterilization and addition to media was exactly the same as for brassinosteroids. 

Sterols are involved in the stabilization of cell membranes (E 2.2). Ergosterol is used in the technical preparation of vitamin Dg (D 6.4.9). Ecdysone and ecdy-sterone are molting hormones in insects and crustaceans (E 3.1). Similar compounds (ecdysteroids), e.g., ponasterone and cyasterone, which are widespread in higher plants, deter feeding insects (E 5.5.3). The hormone activity of certain ecdyste-roids in insects is up to 20 times that of ecdysone. Certain Drosophila species are... 

Wilson (1992) described the use of various boronic acids for the derivatiza-tion and separation of ecdysteroids by normal- and reversed-phase TLC. The derivatives were prepared from butyl-, phenyl-, and aminophenylboronic acids by over-spotting a methanolic solution of the reagent on to the applied ecdysteroids at the origin of the TLC plate. Butylboronic acid was also used as a mobile-phase additive to modify chromatographic behavior. A 20,22-diol group was an essential structural requirement for the formation of a cyclic boronate of an ecdysteroid. These procedures allowed for the selective separations of such compounds as ponasterone A and 2-deoxyecdysone. Pis and Harmatha (1992) also described the use of phenylboronic acid as a versatile derivatization agent for TLC studies of ecysteroids. 

In some arthropods (for this hormone is shared with other classes besides insects), the series are not hydroxylated at C-25. Many crustaceans use 20-hydroxyecdysone as moulting hormone, others use ponasterone A (Figure 7.14). Ecdysteroids have also been found in plants. These phytoecdysteroids are widely distributed in the plant... 

---