The temperature dependence of the binding of 5 alpha-dihydrotestosterone, testosterone and estradiol to the sex hormone globulin (SHBG) of human plasma.
Level 5 - mechanism / opinion, no new human data
In vitro bench research using human plasma
PubMed 3702439 · doi:10.1016/0022-4731(86)90118-4
What was done
The authors measured the binding of 5 alpha-dihydrotestosterone (DHT), testosterone, and estradiol to sex hormone binding globulin (SHBG) and albumin in human plasma at 4, 20, and 37 °C. Binding was evaluated using equilibrium partition in an aqueous two-phase system composed of dextran, polyethylene glycol, and water. Intrinsic association constants for SHBG and apparent association constants for albumin were calculated using Scatchard-type binding plots.
What was found
SHBG affinity was 1.2 to 1.3 times higher for DHT than for testosterone, and 4 times higher for DHT than for estradiol. For all three steroids, binding affinity to SHBG decreased with increasing temperature. Mean free energy of binding (delta G degree) to SHBG across the tested temperatures was -52.3 kJ/mol for DHT, -51.7 kJ/mol for testosterone, and -48.9 kJ/mol for estradiol; corresponding enthalpy change values (delta H degree) were reported as 73.7, 70.0, and 99.0 J/(mol·K). Albumin affinity was nearly equal for testosterone and estradiol, lower than for DHT, and albumin delta G degree of binding was approximately 55% lower than that of SHBG.
Why it matters
This study provides thermodynamic constants quantifying how temperature shifts modulate the binding affinities and free fractions of key circulating sex steroids in human plasma.
Limits
This is strictly an in vitro bench study; donor sample size, sex, and health status are not reported in the abstract. In vitro equilibrium conditions do not capture physiological factors such as competing ligands, protein concentration variations, or in vivo clearance dynamics.
Cited by
- supports Dihydrotestosterone (DHT) has a higher binding affinity for SHBG than testosterone, and testosterone has a higher binding affinity for SHBG than estrogen.