THE MAJOR ACIDIC FIBROBLAST GROWTH-FACTOR (AFGF)-STIMULATED PHOSPHOPROTEIN FROM BOVINE LIVER PLASMA-MEMBRANES HAS AFGF-STIMULATED KINASE, AUTOADENYLYLATION, AND ALKALINE NUCLEOTIDE PHOSPHODIESTERASE ACTIVITIES

The major acidic fibroblast growth factor (aFGF)-stimulated phosphopro tein (MAFP) purified from bovine liver exhibits kinase, autoadenylylat ion, and alkaline nucleotide phosphodiesterase activities depending up on reaction conditions. In the presence of divalent ions, MAFP showed intrinsic and aFGF-stimulated kinase activities (autophosphorylation) using either [gamma-P-32]ATP or [gamma-P-32]GTP as a substrate. The au tophosphorylation activity of MAFP was stimulated at low concentration s of Ca2+, Mg2+, or Mn2+ (0.2-2 muM). Depletion of the divalent ions b y EDTA abolished the autophosphorylation activity but enhanced the aut oadenylylation activity of MAFP. [Alpha-P-32]ATP as well as [alpha-P-3 2]NAD could serve as substrates for autoadenylylation activity of MAFP . aFGF appeared to enhance the autoadenylylation activity of MAFP with an optimal concentration (0.6-1.2 nM). P1,P3-di(adenosine-5')-triphos phate (AP3A) was found to be a potent inhibitor for the autophosphoryl ation and autoadenylylation activities of MAFP. Analyses by automated Edman degradation of the adenylylated and phosphorylated peptides deri ved from autoadenylylated and autophosphorylated MAFP revealed that bo th autoadenylylation and autophosphorylation occurred at residue Thr20 4. The kinase and autoadenylylation activities of MAFP had an optimal pH of 6.9-7.4. However, at pH 8.9, MAFP showed intrinsic and aFGF-stim ulated phosphodiesterase activities. aFGF appeared to stimulate the ph osphodiesterase activity of MAFP without altering the K(m) (approximat ely 0.2 mM) of its substrate.