Myristoyl CoA:protein N-myristoyltransferase: subcellular localization, activation and kinetic behavior in the presence of organic solvents.

Myristoyl CoA:protein N-myristoyltransferase (NMT) catalyses the addition of myristate to the amino terminal glycine residue of a number of cellular, eukaryotic and viral proteins. The majority of the catalytic activity of spleen NMT was recovered in the soluble cytosolic fraction (98.2%) compared to the particulate fraction (19.3%). Recovery of NMT activity, from both cytosol and particulate fractions, was found to be higher than the total activity in crude homogenates, suggesting that the particulate fraction may contain an inhibitory activity towards NMT. The effects of organic solvents (ethanol and acetonitrile) on bovine spleen NMT were investigated. NMT activity was activated several-fold in a time- and concentration-dependent manner in the presence of cAMP-dependent protein-kinase derived peptide substrate as fatty acyl CoA acceptor, suggesting that the activation by organic solvents is not due to a solvent effect. Similar activation by ethanol and acetonitrile was also observed with pp60src as substrate, suggesting that the effect of solvent is on NMT and not on the substrate. Gel filtration chromatography indicated that the high catalytic activity of NMT was observed only in the presence of organic solvents: removal of organic solvents from the medium drastically reduced the catalytic activity of NMT, suggesting that NMT did not undergo covalent modification. Kinetic data indicated that ethanol enhanced the Vmax without affecting the Km.