Zinc chaperone that directly transfers zinc cofactor to target metalloproteins, thereby activating them. Catalyzes zinc insertion into the active site of methionine aminopeptidase METAP1, which function to cleave the initiator methionine from polypeptides during or after protein translation. Mechanistically, the N-terminal psi-PxLVp motif binds to the C6H2-type zinc finger of inactive form of METAP1. After formation of the docked complex, zinc is transferred from the CXCC motif in the GTPase domain of ZNG1B to the zinc binding site in the peptidase domain of METAP1 in a process requiring GTP hydrolysis. GTP/GDP exchange is required for release of active METAP1.