Sammendrag
A sex steroid-binding protein (SBP) that binds 17 beta -estradiol
with high affinity and moderate capacity was identified in the plasma from Arctic charr (Salvelinus alpinus L.) sampled during the early stage of gonadal maturation in June and prior to spawning in October. Maximum
specific binding (B-max) and equilibrium dissociation constant (K-d) of
males (B-max = 2122 fmol E-2/mg protein, K-d = 1.9 nM), females (B-max = 4115 fmol E-2/mg protein, K-d = 3.0 nM), and juveniles (B-max = 4355 fmol
E-2/mg protein, K-d 1.8 nM) resembled binding characteristics of SEP from
related species. The early-maturing females displayed both B-max and K-d
values significantly higher than those of males (June samples). No
significant differences in binding characteristics between fully matured
males or females and immature juveniles were observed in the October
samples. Interestingly, despite large individual variations there was a
strong correlation between SEP levels and affinity. The association rate
for 17 beta -estradiol was rapid (t(1/2) approximate to 1-2 min) compared
with the dissociation rate (t(1/2) approximate to 3 h). Several native
hormones (estrogens, androgens, and progesterone) were able to compete with
tritiated 17 beta -estradiol for the binding site. Gel filtration
chromatography demonstrated a peak of estradiol binding at approximately 60
kDa, when eluted on a Sephadex S-200 HR column. (C) 2001 Academic Press.
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