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1 Department of Medicine,
Montefiore Hospital, and the University of
Pittsburgh School of Medicine,
Pittsburgh, Pennsylvania
The presence of two forms of androgen binding
protein (ABP) was confirmed in rat testicular
cytosol. Each was distinctly separated from the
other by DEAE-cellulose chromatography and
showed a single peak with a slightly different Rf
on polyacrylamide gel electrophoresis (PAGE)
(0.49 ± 0.03 (mean ± SD) for one (ABP I) and
0.55 ± 0.04 for the other (ABP II)). ABP I retained 90% of its binding capacity for dihydrotestosterone for 2 hours at 60 C, whereas
ABP II lost more than 90% of its binding capacity within 10 minutes at 60 C. Other
physicochemical properties of the two were
very similar: identical values of Einstein's
stokes radius of 47 A; sedimentation coefficient
of 4.6 - 4.7 S; 5 - 8 minutes as half dissociation
time of [3H]-dihydrotestosterone-ABP complex;
identical elution positions from Sephadex
G-200 chromatography; and association constants for dihydrotestosterone of 2.1 x 108 M-1
for ABP I and 4.0 x 108 M-1 for ABP II. The order
of binding affinity of the two forms was dihydrotestosterone > testosterone > estradiol-17 
> progesterone. The presence of Ca++ in the
elution buffer caused the two forms to elute at
lower ionic concentration off DEAE-cellulose.
This was reversed by the removal of Ca++ with
the addition of (ethylenebis (oxyethylene nitriio)) tetraacetic acid.
Key words: testis, androgen binding protein, calcium, rat, ABP, dihydrotestosterone
Submitted on August 20, 1979
Revised on November 15, 1979
Accepted on November 16, 1979
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