Binding of uteroglobin to microsomes and plasmatic membranes

Microsomes and plasmatic membranes from rat liver bind radioactive uteroglobin (UG) in vitro with high affinity (Kd = 1.7 x 10(-10) M. The binding is saturable and specific and dependent on previous reduction of UG with dithiothreitol. Microsomes from rat spleen or lung or from rabbit endometrium also possess a similar ability. Binding capacity is not affected by previous treatment of microsomes with phospholipase A2 or peptide-N-glycosidase F but is lost after brief treatment with trypsin. The complex formed between UG and the binding component can be solubilized from microsomes with 5 mM CHAPS and it elutes with an apparent Mr of 90,000 in a Sephacryl 200 column. The complex is resistant to 8 M urea but is completely dissociated by Triton X-100. The UG-binding protein(s) has been partially purified from solubilized microsomes and membranes by affinity chromatography. The results are discussed in relation to a possible physiological effect of UG on cellular membranes.