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Biochemistry. 1995 Jun 13;34(23):7722-7.

Functional significance of beta gamma-subunit carboxymethylation for the activation of phospholipase C and phosphoinositide 3-kinase.

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  • 1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.

Abstract

The gamma subunits of heterotrimeric G proteins are isoprenylated and methylated at their carboxyl-terminal cysteine residues. Since methylation is the only reversible reaction in the isoprenylation pathway, it could be a site of regulation of G protein activity. beta gamma subunits have been shown to activate a number of effectors involved in signal transduction pathways. The methyl group of retinal transducin (T) can be hydrolyzed by an immobilized form of pig liver esterase, allowing for a direct determination of the activities of methylated and demethylated T beta gamma. The abilities of methylated and demethylated T beta gamma to stimulate G protein regulated phosphatidylinositol-specific phospholipase C (PIPLC) and phosphoinositide 3-kinase (PI3K) were determined. It is reported here that there is a strong dependence on methylation for activating both PIPLC and PI3K. Demethylated T beta gamma is at least 10-fold less active than its methylated counterpart. Therefore, methylation may play an important role in the regulation of these effectors and of signal transduction processes in general.

PMID:
7779819
[PubMed - indexed for MEDLINE]

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