STEROIDOGENIC ACTIVITY OF BIOTINYLCORTICOTROPIN-AVIDIN COMPLEXES

The steroidogenic activity of complexes of [biocytin25]-corticotropin1-25 amide (biotinylcorticotropin) with avidin (1:1), (4:1) and (1:10) was compared to that of biotinylcorticotropin using isolated rat adrenal cells. Parallel log-dose responses and maximal stimulation were observed with all these materials. The 1:1 complex is approximately 25% as active as biotinylcorticotropin (ED5022.5 and 5.6 nM respectively). The 4:1 complex is more active than the 1:1 complex (ED509.0 nM). The presence of an excess of avidin (1:10 complex) does not interfere with the ability of biotinylcorticotropin to stimulate steroidogenesis (ED5018.0 nM). It is concluded that biotinylcorticotropin attached to avidin binds specifically to receptors on the rat adrenal cell and elicits its biological response. These results indicate that biotinylcorticotropin can be noninvasively labeled with 125I-avidin. © 1979.