Adds a myristoyl group to the N-terminal glycine residue of certain cellular and viral proteins (PubMed:22865860, PubMed:25255805, PubMed:32686708, PubMed:34999170, PubMed:9353336, PubMed:9506952). Also able to mediate N-terminal lysine myristoylation of proteins: catalyzes myristoylation of ARF6 on both ‘Gly-2’ and ‘Lys-3’ (PubMed:32103017, PubMed:32111831). Lysine myristoylation is required to maintain ARF6 on membranes during the GTPase cycle (PubMed:32103017).