Isolation, characterisation and tissue localisation of an N-terminal-truncated variant of fibroblast growth factor

An additional form of basic fibroblast growth factor (FGF), possessing full biological activity, has been isolated from bovine pituitary extracts. This polypeptide mitogen exhibits an apparent molecular weight of 17,500 by SDS-PAGE and lacks the first four N-terminal amino acid residues (Pro-Ala-Leu-Pro) of a previously described FGF preparation. Polyclonal antibodies have been raised to this FGF variant and used to examine the distribution of immunoreactive FGF species in rat and bovine tissues by immunoblot procedures. In extracts of rat pituitary, kidney, spleen and liver tissues several higher molecular weight species were detected with immunoreactive 70 kDa and 27 kDa protein bands predominating whilst a 32 kDa immunoreactive protein was also present in the brain. In bovine tissues several immunoreactive proteins with molecular weights greater than 17,500 were also observed in the brain, pituitary, adrenal, ovary and serum with these immunoblot procedures. With bovine pituitary extracts, six immunoblot bands corresponding to immunoreactive proteins of molecular weights 80,000-14,200 were observed, whilst with the brain extracts four immunoblot bands and with serum eight immunoblot bands ranging from 150,000 to 14,200 were detected. With non-immune rabbit serum, no polypeptides/proteins of corresponding molecular weight could be detected with similar immunoblot procedures. The possible relationships of these immunoreactive proteins to FGF precursor forms at various stages of processing are described.