Purification and partial sequencing of myristoyl-CoA:protein N-myristoyltransferase from bovine brain

Abstract

The enzyme myristoyl-CoA:protein N-myristoyltransferase (NMT; EC 2.3.1.97) catalyses the transfer of myristic acid to the N-terminal glycine residue of cell and viral proteins. In this report the purification and partial sequencing of this enzyme from bovine brain is described. Using a combination of ammonium sulphate precipitation, chromatography on DEAE-Sepharose and affinity chromatography on CoA-agarose the enzyme was purified some 40-fold. Size-exclusion chromatography of this material in the presence of myristoyl-CoA yielded two peaks of enzyme activity with apparent molecular masses of 66 kDa and 43 kDa. Chromatography of the CoA-affinity-purified material on MONO-S followed by size-exclusion chromatography in the presence of myristoyl-CoA resulted in the isolation of the large form of the enzyme purified 3000-fold. Analysis by SDS/PAGE of this material showed a major 60 kDa silver-stained band. Similar analysis of the 43 kDa enzyme fraction from the same separation showed that this fraction contained several proteins including a major component with an apparent molecular mass of 49 kDa. Attempts at N-terminal sequencing of the 66 kDa form of the enzyme were unsuccessful and therefore this material was digested with trypsin and the resulting peptides separated by reverse-phase h.p.l.c. N-terminal protein sequencing of these peptides yielded sequences which show sequence similarity to those of yeast N-myristoyl-transferase.