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Polyethylene glycol‐stimulated microsomal GTP hydrolysis
Author(s) -
Nicchitta Christopher V.,
Joseph Suresh K.,
Williamson John R.
Publication year - 1986
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(86)81120-6
Subject(s) - gtp' , gtpase , microsome , peg ratio , polyethylene glycol , chemistry , biophysics , cytosol , biochemistry , g protein , enzyme , biology , receptor , finance , economics
It has recently been observed that GTP mediates Ca 2+ release from internal Ca 2+ stores. In contrast to effects on permeabilized cells, GTP‐dependent Ca 2+ release in isolated microsomes requires the presence of polyethylene glycol (PEG). We have investigated the effects of PEG on microsomal GTPase activity and report that PEG stimulates a high‐affinity ( K m = 0.9 μM) GTPase. The effects of PEG reflect an increase in the V max of this activity; no effects on K m were observed. The concentration dependence for PEG‐dependent stimulation of the high‐affinity GTPase exactly mimicked that for GTP‐dependent Ca 2+ release. The stimulation of GTP hydrolysis by PEG was specific for the microsome fraction; only small effects were obtained with plasma membrane or cytosol fractions. As observed for GTP‐dependent Ca 2+ release, the microsomal PEG‐stimulated GTPase was competitively inhibited by the GTP analog GTPγS ( K i = 60 nM). It is proposed that the PEG‐stimulated GTPase may represent an intrinsic activity of the guanine nucleotide binding protein involved in the regulation of reticular Ca 2+ fluxes.