The alpha-subunits of G-proteins G12 and G13 are palmitoylated, but not amidically myristoylated.

The alpha-subunits of the G-proteins G12 and G13 were expressed with a baculovirus system in insect cells and analysed for acylation. Both proteins incorporated tritiated palmitic and to a lesser extent also tritiated myristic acid. Radiolabel from both fatty acids was sensitive to treatment with neutral hydroxylamine. This result supports a thioester-type fatty acid bond and argues against amidical N-myristoylation. Fatty acid analysis after labeling with [3H]palmitic acid showed that palmitate represents the predominant fatty acid linked to G alpha 12 and G alpha 13. Separation of cells into cytosolic and membranous fractions revealed that palmitoylated alpha-subunits of G12 were exclusively membrane-bound, whereas [35S]methionine-labeled proteins were detected in soluble and particulate fractions. Inhibition of protein synthesis with cycloheximide did not block palmitoylation of the alpha-subunits, which indicates that palmitoylation occurs independently of protein synthesis.