Formation Of Unidentified Products Research Articles

Conversion of different putative ecdysteroid precursors in Lithobius forficatus L. (Myriapoda: Chilopoda)

The biosynthetic pathway of ecdysteroids has been investigated in the centipede Lithobius forficatus. By using various labeled putative precursors already known to be efficiently converted into ecdysone and 20-hydroxyecdysone by insects and crustaceans, it was found that the reactions always stopped at 2-deoxyecdysone, and that this compound was only epimerized and conjugated at the C-3 position. Ecdysone was efficiently converted into 20-hydroxyecdysone, whereas 20-hydroxylation was not effective with 2-deoxyecdysteroids. None of the tested precursors was hydroxylated at the C-2 position. In addition, in vivo labeling experiments with [ 3H]cholesterol led only the formation of unidentified products. Therefore, the origin of the already reported ecdysone and 20-hydroxyecdysone in these animals remains still conjectural. The “ecdysial glands” (i.e. the putative molting glands) and gonads proved the most effective tissues to convert 2,22,25-trideoxyecdysone into 2-deoxyecdysone in vitro, although at rather low levels. By contrast, this compound was very efficiently converted in vivo. The present data raise many unanswered questions, and they point out that classical inserct schemes are not applicable in the present case. It might thus well be that divergent pathways have evolved in arthropods, and this problem awaits further investigations.

The Radiolysis of Nitrate Ions Dispersed in a Potassium Bromide Matrix

Data are presented on the radioinduced decomposition of nitrate ions dispersed in a potassium bromide lattice. It is shown that the nitrite ion found in an aqueous solution of the irradiated solid existed in the solid prior to dissolution and did not arise by reaction of stabilized intermediates with the water. The equivalence of the initial slopes of the curves for the decomposition of nitrate ion and the formation of nitrite ion confirms this result. It is shown that no equilibrium can be obtained during the decomposition of the nitrate ion because it is decomposed when dispersed in a KBr lattice with the formation of unidentified products which do not recombine to form an equivalent amount of nitrate ion. This means that it is not possible to equate the amount of nitrite ion found after irradiation with the amount of nitrate ion decomposed. It is shown that oxygen atoms diffuse within the potassium bromide lattice, since some nitrate ion is produced during the decomposition of the nitrite ion. (auth)