The structure of a juvenile hormone-binding lipophorin from the hemolymph of Diploptera punctata

The high molecular weight, high affinity juvenile hormone binding protein from the hemolymph of Diploptera punctata was identified as a lipophorin by gradient KBr ultracentrifugation and SDS gradient PAGE. This juvenile hormone binding lipophorin (JHBL) was composed of two subunits, apolipoprotein I (230 kDa mol. wt) and apolipoprotein II (80 kDa mol. wt). The density of the native protein was 1.15 g/ml. Photoaffinity labeling using the JH analog ³H]EFDA demonstrated that the JH binding site resides on apolipoprotein I. The amino acid composition of both native lipophorin and its two subunits was determined and the N-terminal sequence of the 80 kDa apolipoprotein described for 19 of the first 21 amino acids. This sequence did not have similarity to any known protein. The N-terminus of the 230 kDa apolipoprotein was blocked. The specificity of a monoclonal antibody to purified native JHBL was also demonstrated. We show that the monoclonal antibody was specific to the 230 kDa subunit and did not recognize the 80 kDa apolipoprotein.