Physico‐chemical properties of the hydroxysterol binding protein of human lymphocyte cytosol

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Abstract
Side chain-hydroxylated derivatives of cholesterol (OH sterol) inhibiting lymphoblastic transformation bind with high affinity and specificity to a hydroxysterol binding protein (OHSBP) in the cytosol of human lymphocytes. These binding properties of OHSBP suggested some analogies with that of steroid hormone receptors. The observation of a nuclear binding of 25-OH[3H]cholesterol prompted us to apply to the cytosolic OH sterol-OHSBP complex the physico-chemical treatments known to ‘activate’ the steroid hormone receptors. A change of sedimentation coefficient from 8.3 to 4.3 S was observed in hypertonic buffer (0.4 M KC1) but the resulting 4.3 S complex dissociates easily whereas the ‘native’ 8.3 S form does not. Moreover, molybdate did not prevent the 8.3→ 4.3 S transformation induced by KCland neither ammonium sulfate precipitation nor increasing temperature had any effect on the sedimentation coefficient of the 8.3 S complex. Thus, several physico-chemical features differentiate the OH sterol-OHSBP complex from steroid hormone receptors.HydroxysterolHuman lymphocyteSpecific binding proteinCell divisio