Co-purification of a ribonuclease and human chorionic gonadotrophin 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 electrophoretic homogeneity as judged by sliver-staining of polyacrylamide gels, inhibited binding of I-125-hLH (human luteinizing hormone) to Candida albicans microsomes, reacted with monoclonal and polyclonal antibodies 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 identical to those of the N-terminus of human non-secretory ribonuclease. These results indicate co-purification of hCG beta-core with a RNase. An 18 kDa RNase was also purified from a commercial hCG preparation (Chorulon). However, no RNase activity was detected in a highly purified commercial preparation (Profasi). Three commercial RNase preparations displaced I-125-hLH from C. albicans binders at extremely low concentrations (< 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 to the close relationship that has been identified between mammalian RNase inhibitors and the extracellular domain of gonadotrophin receptors. The presence of RNase in commercial preparations of gonadotrophins should be borne in mind during any investigations that involve impure preparations of these hormones. (C) 1997 Elsevier Science Ireland Ltd.