title: Affinity labelling of human transcortin.
abstract: The binding site of transcortin has been studied by using bromoacetyltestosterone and bromoacetylated derivatives of progesterone which were monohydroxylated at different positions of the steroid nucleus. Specificity of affinity labelling was demonstrated by the displad cortisol analog was added to a [3H]cortisol-transcortin complex solution. The binding site crevice was found to be very narrow in the vicinity of the A and B rings of steroid since 2alpha-hydroxyprogesterone, 6alpha- or 6beta-bromoacetoxyprogesterone and dexamethasone could not displace bound cortisol. A specific affinity labelling was obtained with 11alpha-bromoacetoxyprogesterone, 16alpha-bromoacetoxyprogesterone and 17beta-bromoacetyltestosterone. The results of the affinity labelling by these hormone analogs suggested that one methionine and one histidine residues were located within the active site:methionine might interact with the 11beta-hydroxyl group and histidine with the 20 keto group of cortisol.
mesh_terms: D000345:Affinity Labels; D000596:Amino Acids / Q000032:analysis; D001665:Binding Sites; D001667:Binding, Competitive; D006801:Humans; D006854:Hydrocortisone; D006908:Hydroxyprogesterones; D007700:Kinetics; D008968:Molecular Conformation; D011374:Progesterone / Q000031:analogs & derivatives; D013329:Structure-Activity Relationship; D014156:Transcortin
chemical_list: D000345:Affinity Labels; D000596:Amino Acids; D006908:Hydroxyprogesterones; D011374:Progesterone; D014156:Transcortin; D006854:Hydrocortisone