Humic substances are important components of soil systems. The reaction between enzymes and soluble humic matter has been attributed to co-polymerization, adsorption and encapsulation of enzymes into the inner structure of HS. The importance of electrostatic and hydrophobic interactions between humic acids and proteins concluded that parameters like mixing ratio of HA and protein, pH and ionic strength determined the extent of HA-protein complexation and aggregation of the complexes. For PAHA-lysozyme complexation, the aggregate size is at its maximum at the IEP of the complexes. At mass ratios beyond the IEP the aggregates partially disaggregate. Mixing of LSZ and PAHA is initially enthalpically driven. Near the IEP complexation and aggregation are due to hydrophobic forces (structural re-organization) and counterion release. The enzyme activities in the HS-enzyme complexes were suppressed when the enzymes were oppositely charged to the HS. The largest activity suppression was observed around the mass ratio HS/enzyme where the HS-protein complex was at its isoelectric point (Fig. 1). At the IEP strong aggregation of the complexes led to encapsulation of the enzyme. The ionic strength was important; an increase decreased complex formation, but increased aggregation. Due to the larger hydrophobicity of JGHA than JGFA, the reduction in enzyme activity was stronger for JGHA. The enzyme stability decreased also maximally at mass ratio around the IEP of the complex when HS and protein were oppositely charged. When urease and HS were both negatively charged no complexes were formed, but the presence of JGHA or JGFA improved the activity and stability of the enzyme.Fig. 1 The activity of lysozyme depends on the mass ratio of HS/LSZ and ionic strength

Interaction of protein with humic aicd

248th National Meeting (2014)

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