Journal of Neuroscience, Vol 4, 99-110, Copyright © 1984 by Society for Neuroscience
DARPP-32, a dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein enriched in dopamine-innervated brain regions. II. Purification and characterization of the phosphoprotein from bovine caudate nucleus
HC Hemmings Jr, AC Nairn, DW Aswad and P Greengard
DARPP-32 is a neuronal phosphoprotein of Mr = 32,000, originally identified
in rat brain (Walaas, S.I., D.W. Aswad, and P. Greengard (1983) Nature 301:
69-72). This protein has now been identified in bovine caudate nucleus
cytosol and purified 435-fold to apparent homogeneity as judged by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis. The purification
procedure involved acid extraction at pH 2, CM-cellulose chromatography,
DEAE-cellulose chromatography, hydroxylapatite chromatography, and gel
filtration on Ultrogel AcA 44. The purified catalytic subunit of
cAMP-dependent protein kinase catalyzed the incorporation of 0.96 mol of
phosphate/mol of purified DARPP-32. Phosphorylation occurred exclusively on
threonine. The isoelectric point of dephospho-DARPP-32 was 4.7, and that of
phospho- DARPP-32 was 4.6. The amino acid composition showed a high content
of glutamate/glutamine and proline, and a low content of hydrophobic amino
acids. DARPP-32 was found to have a Stokes radius of 34 A and a
sedimentation coefficient of 2.05 S, indicating that it exists as an
elongated monomer.