Ecdysteroids are bound to vitellin in newly laid eggs of Locusta.

The follicle cells of vitellogenic ovaries of Locusta migratoria have been reported to synthesize impressive amounts of ecdysteroids which accumulate inside the oöcytes where they persist during egg-laying; these ecdysteroids are conjugated to more than 95%, and it is believed that their hydrolysis in the egg is the source of the peaks of free ecdysone observed in early embryonic development. The present paper shows that, in the eggs, the ecdysteroid conjugates are bound to a 520 000-dalton macromolecule which shares several characteristics with the major yolk protein vitellin and is precipitated by an anti-vitellin antibody. The physiological relevance of the binding of ovarian ecdysteroid conjugates is discussed in respect to the transfer of maternal ecdysteroids to the embryo.