CHARACTERIZATION OF AZADIRACHTIN BINDING TO SF9 NUCLEI IN-VITRO

[22,23-H-3(2)]dihydroazadirachtin was incorporated by Sf9 cells in cul ture and was bound specifically to the nuclear fraction. The observed association constant of the binding of the radioligand to a purified n uclear fraction was determined to be 0.037 +/- 0.008 min(-1) using a o ne-phase exponential association equation, and binding appeared to be to a single population of sites. The binding was essentially irreversi ble, and the dissociation constant was estimated to be 0.00065 +/- 0.0 0013 min(-1). An association rate constant of 7.3 x 10(6) M(-1) min(-1 ) was calculated from these data. Binding was saturable, and the recep tor number and affinity were determined as B-max = 23.87 +/- 1.15 pmol /mg protein, K-d = 18.1 +/- 2.1 nM. The order of potency of semisynthe tic azadirachtin analogues for competition for the binding site was as follows (IC50 in parentheses): azadirachtin (1.55 x 10(-8) M) > dihyd roazadirachtin (3.16 x 10(-8) M) > dansyl dihydroazadirachtin (7.40 x 10(-8) M) > DNP-azadirachtin (7.50 x 10(-8) M) > biotin dihydroazadira chtin (1.27 x 10(-7) M) much greater than ll-methoxy 22,23-dihydroazad irachtin (6.67 x 10(-7) M). (C) 1997 Wiley-Liss, Inc.