The enzyme participates in the N-end rule protein degradation pathway in certain bacteria, by attaching the primary destabilizing residue L-leucine to the N-termini of proteins that have an N-terminal L-aspartate or L-glutamate residue. Once modified, the proteins are recognized by EC
3.4.21.92, the ClpAP/ClpS endopeptidase system. cf. EC
2.3.2.6, lysine/arginine leucyltransferase, and EC
2.3.2.8, arginyltransferase.