Purification of follicular regulatory protein: Possible plasminogen identity

A partially purified protein (the SR fraction) of porcine and human origin has been extensively characterized as Follicular Regulatory Protein (FRP). In the current study, 1A8D5, one of several monoclonal antibodies raised ag ainst FRP, was used to further purify the protein. The monoclonal antibody cross-reacted only with porcine plasminogen, a key fibrinolytic proenzyme. A commercial polyclonal antibody for human plasminogen confirmed the relati onship between plasminogen and bands of the SR fraction of the porcine foll icular fluid. Sequencing of the N-terminal amino acids (54 kd) of the SR fr action indicated that it shared 100% identity with the short form of porcin e plasminogen chain A and 93% identity to human plasminogen. Moreover, we d emonstrated that this purified protein from human follicular fluid inhibite d aromatase activity of granulosa cells, a key biological property of FRP. Given that plasminogen possesses most of the proposed properties of the pro tein termed FRP, we conclude that FRP is likely plasminogen itself or a pla sminogen-related protein and not a novel protein. (C) 2001 Academic Press.