During an examination of in vitro phosphorylation of the adipocyte lipid-binding protein (ALBP) by the insulin receptor, we detected insulin receptor-independent, chemical phosphorylation of ALBP. This activity was present in ALBP purified to homogeneity from murine 3T3-L1 cells and in recombinant murine ALBP purified from expressing E. coli cultures. Phosphoamino acid analysis revealed that chemical phosphorylation of ALBP occurred primarily on Ser residues. The phosphorylation activity occurred in the alkaline pH range from 8 to 11 and exhibited a broad temperature dependence. The reaction rate was linearly dependent upon the ATP concentration and exhibited a biphasic kinetic profile. Eight of twelve other proteins tested also underwent chemical phosphorylation. Zn+2, Mg+2, or Mn+2promoted optimal phosphorylation of different proteins. We conclude that many proteins are capable of undergoing chemical phosphorylation. © 1989.
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