COPURIFICATION OF A RIBONUCLEASE AND HUMAN CHORIONIC-GONADOTROPIN BETA-CORE PROTEIN FROM HUMAN URINE AND DISPLACEMENT OF I-125 HUMAN LUTEINIZING-HORMONE FROM CANDIDA-ALBICANS BINDING-SITES BY RIBONUCLEASES

An 18 kDa pregnancy urine protein preparation, purified to apparent el ectrophoretic homogeneity as judged by sliver-staining of polyacrylami de gels, inhibited binding of I-125-hLH (human luteinizing hormone) to Candida albicans microsomes, reacted with monoclonal and polyclonal a ntibodies raised against human chorionic gonadotrophin (hCG) beta-core protein and exhibited ribonuclease (RNase) activity. Eleven of the 12 amino acids at the N-terminus of a protein in this preparation were i dentical to those of the N-terminus of human non-secretory ribonucleas e. These results indicate co-purification of hCG beta-core with a RNas e. An 18 kDa RNase was also purified from a commercial hCG preparation (Chorulon). However, no RNase activity was detected in a highly purif ied commercial preparation (Profasi). Three commercial RNase preparati ons displaced I-125-hLH from C. albicans binders at extremely low conc entrations (< 0.001 mu g/ml RNase) whereas only slight displacement of I-125-hLH from sheep luteal binding sites was observed with very high concentrations of the RNases (100 mu g/ml RNase). The co-purification of hCG beta-core and RNase from pregnancy urine and the displacement of I-125-hLH from C. albicans binding sites by RNases may be related t o the close relationship that has been identified between mammalian RN ase inhibitors and the extracellular domain of gonadotrophin receptors . The presence of RNase in commercial preparations of gonadotrophins s hould be borne in mind during any investigations that involve impure p reparations of these hormones. (C) 1997 Elsevier Science Ireland Ltd.