A GTP-binding peptide regulates beta-adrenergic response of adenylate cyclase

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We found a cytosolic peptide with a relative molecular weight (Mr)-3,000 in the rat liver which binds to GTP to potentiate the GTP effect on beta-adrenergic response of adenylate cyclase. In the present study, the peptide was purified and characterized. The peptide was isolated as a complex form with GTP on a Sephadex G-25 column in a low salt solution, and was purified as a dissociated form on the column in a high salt solution. The photoaffinity-labeling using [alpha^<-32>P]GTP of the fraction which on the second column showed GTPgammaS-binding activity as well as an enhancing activity of the GTP effect demonstrated that the 3,000 Mr peptide has the GTP-binding property. The fraction was further purified on reverse phase (C_<18>) HPLC.Two peak fractions (fractions I,II) with GTPgammaS-binding activity were obtained, and fraction I eluted with a lower percentage of acetonitrile, enhanced the GTP (10^<-5>) effect maximally 4.8 fold. The amino acid composition analysis of these fractions displayd that fractions I and II are leucine (17 mol/100 mol)- and glycine (34 mol/100 mol)-rich, respectively. To know the primary structure of these peptides, amino acid sequence analysis and the cloning of cDNA are needed.