Lactonase (EC 3.1.1.81, acyl-homoserine lactonase; systematic name N-acyl--homoserine-lactone lactonohydrolase) is a metalloenzyme, produced by certain species of bacteria, which targets and inactivates acylated homoserine lactones (AHLs). It catalyzes the reaction
: an N-acyl--homoserine lactone + HO  an N-acyl--homoserine
Many species of α-, β-, and γ-proteobacteria produce acylated homoserine lactones, small hormone-like molecules commonly used as communication signals between bacterial cells in a population to regulate certain gene expression and phenotypic behaviours. This type of gene regulation is known as quorum sensing.
Other names for these types of enzymes are Quorum-quenching N-acyl-homoserine lactonase, acyl homoserine degrading enzyme, acyl-homoserine lactone acylase, AHL lactonase, AHL-degrading enzyme, AHL-inactivating enzyme, AHLase, AhlD, AhlK, AiiA, AiiA lactonase, AiiA-like protein, AiiB, AiiC, AttM, delactonase, lactonase-like enzyme, N-acyl homoserine lactonase, N-acyl homoserine lactone hydrolase, N-acyl-homoserine lactone lactonase, N-acyl--homoserine lactone hydrolase, quorum-quenching lactonase, quorum-quenching N-acyl homoserine lactone hydrolase.