Distinct guanine nucleotide binding and release properties of the three Gi proteins

J Biol Chem. 1990 Apr 15;265(11):6268-73.


The native pertussis toxin sensitive GTP-binding proteins (Gi proteins) were individually resolved, and their guanine nucleotide binding and release properties were studied. Gi2 and Gi3, the two major GTP-binding proteins of human erythrocytes, were purified to apparent homogeneity by fast protein liquid chromatography. Gi1 was purified from bovine brain. The three proteins bound 0.6-0.85 mol of guanosine 5'-O-(thio-triphosphate (GTP gamma S)/mol of protein with similar affinities (KD(app) = 50-100 nM). The rate of [35S]GTP gamma S binding to Gi2 was 5-8-fold faster than to Gi1 or Gi3 at 2 mm Mg2+. There were no observable differences in the binding characteristics between bovine brain Gi1 and human erythrocyte Gi3. At 50 mM Mg2+, all three Gi proteins exhibited fast binding, although Gi1 and Gi3 were marginally slower than Gi2. All three Gi proteins exhibited different rates of [32P]GDP release at 2 mM Mg2+. GDP release from Gi2 was severalfold faster than that from Gi1 or Gi3. GDP release rates from Gi1 and Gi3 were similar, although Gi3 was somewhat (60-80%) faster than Gi1. These data indicate that rates of GDP release and GTP binding may be independently regulated for these three proteins and that the relative proportions of Gi2/Gi1 or Gi2/Gi3 will be a crucial factor in determining the kinetics of signal transduction through Gi-coupled effectors.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Brain / metabolism*
  • Cattle
  • Erythrocytes / metabolism
  • GTP-Binding Proteins / blood
  • GTP-Binding Proteins / isolation & purification
  • GTP-Binding Proteins / metabolism*
  • Guanine Nucleotides / metabolism*
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Guanosine Diphosphate / metabolism*
  • Guanosine Triphosphate / analogs & derivatives*
  • Guanosine Triphosphate / metabolism
  • Humans
  • Kinetics
  • Software
  • Thionucleotides / metabolism*


  • Guanine Nucleotides
  • Thionucleotides
  • Guanosine Diphosphate
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Guanosine Triphosphate
  • GTP-Binding Proteins