J. Biol. Chem., Vol. 255, Issue 1, 310-317, 01, 1980
Partial purification and characterization of reticulocyte phosphatase with activity for phosphorylated peptide initiation factor 2
N Grankowski, D Lehmusvirta, G Kramer and B Hardesty
An enzyme fraction containing phosphatase activity for phosphorylated
eukaryotic peptide initiation factor 2 (eIF-2) has been isolated from
rabbit reticulocytes and partially characterized. The enzyme efficiently
catalyzes release of phosphate from the small subunit of eIF-2 (eIF-2
alpha) that has been phosphorylated by the hemin- controlled repressor. It
is shown to restore activity of this phosphorylated eIF-2 for binding of
methionyl-tRNAf to 40 S ribosomal subunits in a partial reaction of peptide
initiation. The enzyme fraction also has phosphatase activity for eIF-2
phosphorylated in its largest subunit and for the 100,000-dalton peptide
associated with the eIF-2 alpha kinase activity of the hemin-controlled
repressor. The phosphoprotein phosphatase has been isolated by a procedure
involving precipitation with ethanol at room temperature and has an
apparent molecular weight in the order of 76,000. Its phosphatase activity
for eIF-2 alpha is stimulated about 3-fold by optimal concentrations of
Mn2+, but is not stimulated by Ca2+ or Mg2+. The enzyme is strongly
inhibited by Fe2+ and by purine nucleoside diphosphates.
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