Question

A) what is the kd for hormone binding by protein 2 (include the units)?

Answer 1

Sex hormone‑binding globulin (SHBG) is the blood transport protein for testosterone and estradiol. It is a large glycoprotein with a molecular weight of about 95 kD, and exists as a homodimer composed of two identical subunits. Each subunit contains two disulfide bridges.

Planar C18 and C19 steroids with a 17α‑hydroxyl group bind particularly well, whereas C19 17‑ketosteroids such as dehydroepiandrosterone (DHEA) and androstendione do not bind so easily. SHBG has a high binding affinity to dihydrotestosterone (DHT), medium affinity to testosterone and estradiol, and only a low affinity to estrone, DHEA, androstendione, and estriol. SHBG binds reversibly to sexual steroids. Albumin, which exists in far higher concentrations than SHBG, also binds sexual steroids – although with a clearly lower binding affinity (e.g. about 100 times lower for testosterone).

SHBG has a half - life of about 7 days and is produced mainly by the liver. Its synthesis and secretion are regulated by estrogen. SHBG serum concentrations depend on the extent, duration, and the kind of estrogen applied, and how regulation takes place. Androgens and gestagens with androgenic residual action have the opposite effect.