An inhibitor from placenta specifically binds urokinase and inhibits plasminogen activator released from ovarian carcinoma in tissue culture

An inhibitor present in placenta and released in placental tissue culture forms specific complexes with each of two molecular forms of urokinase. Audoradiography demonstrated that the inhibitor shifted the electrophoretic position of ¹²⁵I-labelled urokinase. It did not change the migration of diisopropyl-fluorophosphate-inactivated ¹²⁵I-labelled urokinase, thereby indicating complex formation dependent on active serine site in urokinase. The inhibitor had a strong neutralizing effect on the plasminogen activators released from human ovarian carcinoma in tissue culture. The placental inhibitor might prove useful in inhibiting the fibrinolytic process necessary for proliferation of tumour vessels.     

A lymphoma protein with an in vitro site of tyrosine phosphorylation homologous to that in pp60src

The major in vitro substrate for a tyrosine protein kinase in the particulate fraction of the lymphoma cell line LSTRA is a protein of molecular weight of 58,000 (pp58) (Casnellie, J. E. Harrison, M. L., Pike, L. J., Hellstrom, K. E., and Krebs, E. G. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 282-286). In order to determine if this protein was related to pp60src, the transformation-specific protein from Rous sarcoma virus, partial proteolysis maps of in vitro 32P-labeled pp58 and pp60src were prepared using Staphylococcus aureus V8 protease and papain. The maps were clearly different, indicating the pp58 is distinct from pp60src. However characterization of the tryptic fragment containing the single site of in vitro tyrosine phosphorylation in pp58 has revealed that the amino acid sequence around this site is extremely homologous to, if not identical with the sequence around the site of tyrosine phosphorylation in pp60src.