BINDING OF UTEROGLOBIN TO MICROSOMES AND PLASMATIC MEMBRANES

Microsomes and plasmatic membranes from rat liver bind radioactive uteroglobin (UG) in vitro with high affinity (K-d = 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 A(2) 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 M(r) 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.