J. Biol. Chem., Vol. 261, Issue 27, 12568-12573, Sep, 1986
Presence of a MgATP/ADP-dependent pp50 phosphatase in bovine brain coated vesicles
A Pauloin and P Jolles
Coated vesicles are involved in the intracellular transport of membrane
proteins between a variety of membrane compartments in which they must be
able to undergo repeated membrane fusion and fission. We previously
described the presence of cyclic nucleotide- and Ca2+-independent protein
kinase activity in bovine brain coated vesicles which specifically
phosphorylated a unique Mr = 50,000 coated vesicle integral protein (pp50)
on a threonine residue. We describe now the presence in bovine brain coated
vesicles of the antagonistic enzymatic activity which dephosphorylates
pp50. This phosphoprotein phosphatase occurs under two interconvertible
active and inactive forms. The activation process needs the simultaneous
presence of Mg2+ and ATP or ADP. Unchelated ATP, but not unchelated ADP,
inactivates the pp50 phosphatase. The latter is associated with the
vesicular core. MgADP activation of the pp50 phosphatase implicates a
different mechanism which does not need a phosphorylated intermediate.
Thus, the pp50 phosphatase might belong to a new phosphatase type distinct
from the four other classes of well known protein phosphatases.