To characterize the transformation of extracellular proteins extracted from raw and enzymedisintegrated waste activated sludge (WAS), extracts of extracellular polymeric substances (EPS) were subject to isobaric tags for relative and absolute quantitation (iTRAQ) proteomics analysis. 209 proteins were identified and categorized into three Gene Ontology classifications: "cellular components", "molecular function", and "biological processes". Most identified proteins originated from intracellular components, organelles, or cytoplasm, suggesting that cell decline and lysis represent the main sources of extracellular proteins in WAS. The major protein functions comprised "transporter binding activity", "macromolecule metabolic process", and "biosynthesis enzyme catalytic activity". In total, 15 proteins categorized as "membrane part" and "biological adhesion" and 10 as "organelle" were down-or up-regulated, respectively, implying that the enzyme-disintegration mainly induced WAS floc-structure disintegration via membrane structure and corresponding biological adhesion disruption. The proteomics study will provide valuable clues to better understand EPS changes associated with enzymatic treatment at molecular levels. (C) 2016 Elsevier Ltd. All rights reserved.