Inhibition of yolk formation in locust oocytes by trypan blue and suramin.

Trypan blue and suramin inhibit receptor-mediated endocytosis of vitellogenin in Locusta migratoria. Both drugs bind to cationic side chains of the vitellogenin molecule, which are presumably also the binding sites for the specific vitellogenin receptor. Thus binding of vitellogenin to the receptor is prevented in isolated oocytes and in oocyte membrane preparations. Small amounts of trypan blue may unspecifically enter oocytes by "piggy-back" endocytosis. Suramin has a high affinity for vitellogenin and in contrast to trypan blue it does not form insoluble complexes with the protein. Therefore, it may be a useful tool for further analysis of the locust vitellogenin receptor.