Sex steroid binding proteins in fish

TL;DRAbstract

A sex steroid binding protein (SBP) binding E2 with high affinity has been detected in the pleuronectid greenback flounder (Rhombosolea tapirina), the sparids black bream (Acanthopagrus butcheri) and snapper (Pagrus auratus), and its presence has been confirmed in the salmonid rainbow trout (Oncorhynchus mykiss). SBP binding characteristics were measured using a hot saturation assay for trout, bream and snapper and a cold saturation assay for flounder. Bound and unbound steroid were separated by incubation with dextran-coated charcoal (DCC). Affinity for E2 was highest in trout (kD=0.44 nM), followed by bream (kD=3.39 nM) and snapper (kD=10.7 nM). The lowest affinity was found in flounder (kD=84.7 nM). Binding capacity, however, was greatest in flounder (Bmax=164 nM), followed by trout (Bmax=92 nM), and then bream and snapper (Bmax=50 and 39 nM, respectively). Binding of E2 to SBP had a very rapid rate of association, and most dissociation occurred within 5 min. To confirm that the pla

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