Tomaszewski JE Schwarzenbach RP Sander M 2011 Protein encapsulation by natural organic matter is hypothesized to preserve the activity of proteins in terrestrial and aquatic environments. Direct molecular-level evidence for encapsulation of net positively charged proteins lysozyme, trypsin, and ribonuclease A by a diverse set of humic substances (HS) in nanostructured films was collected using a combination of optical waveguide lightmode spectroscopy and quartz crystal microbalance measurements. The results suggest that protein-HS electrostatic attraction drives encapsulation of positively charged lysozyme by a soil humic acid at pH 5 to 8 and by six additional humic and fulvic acids from terrestrial and mixed terrestrial aquatic sources at pH 5 and 6. Encapsulation of trypsin and ribonuclease A, which had negatively charged surface patches under the studied conditions, suggested that localized protein-HS electrostatic repulsion is overcompensated by attractive forces, likely including contributions from the hydrophobic effect. Evidence is provided showing that encapsulation of lysozyme at pH 8 and of ribonuclease A at pH 5 and 6 involved partial disassembly of HA supramolecular associations. This work advances a molecular-level picture of protein encapsulation by HS and presents a novel approach to study the effects of encapsulation on protein enzymatic activity and susceptibility to abiotic and biotic transformations. https://sonar.ch/global/documents/199170 eng info:eu-repo/semantics/altIdentifier/doi/10.1021/es200663h info:eu-repo/semantics/altIdentifier/pmid/21678916 Environmental science & technology. - 2011 Biotransformation Humic Substances Hydrogen-Ion Concentration Models, Molecular Muramidase Nanostructures Proteins Quartz Crystal Microbalance Techniques Ribonuclease, Pancreatic Spectrum Analysis Static Electricity Trypsin Protein encapsulation by humic substances. http://purl.org/coar/resource_type/c_6501