Humic substances is a generic term to indicate relatively high molecular weight, brown to black colored substances formed by secondary condensation reactions, negatively charged, branched polyelectrolytes with mainly carboxylic and phenolic functional groups. Humic substances are ubiquitary in nature. The classical view of humic substances shares three basic fractions termed humic acids (soluble at alkaline pH values), fulvic acids (soluble at a wide range of pH values) and humine (insoluble in water at any pH). Considerable uncertainty still exists regarding the molecular weight and structure of humic substance. The main accepted model is the supramolecular structure, and regardless of their molecular structure, they constitute 70-80% of the soil organic matter. It is well kwon that proteins in the soil ecosystem interact with the solid phases, either inorganic (e.g. clays) or organic (e.g. humic acids). While interactions between proteins of various origin with clays has been widely studied, interactions between proteins and humic substances is considerably less characterized. Most of the information on this topic is based on the extraction of humic-enzymatic complexes, which have been proved to preserve the enzymes from chemical degradation or hydrolysis. To understand the modes of interactions between microbial proteins and humic substances, we undertook a multidisciplinary study based on the behaviour of humic substances of various origin, with a purified ?-glucosidase from the soil-borne fungus Aspergillus niger. Chemical interactions between the enzyme and humic substances was studied using a quartz microbalance (Kinetica, Elba Tech), which indicates the eventual formation of chemical bonds. Effects of the humic substances on the enzyme activity was studied through native gel electrophoresis and visualization of the enzyme activity by staining with 4-Methylumbelliferyl-beta-D-glucopyranoside. The preliminary results show that under the tested conditions, the formation of enzyme-humic substances complexes requires specific factors to occur, and that the ?-glucosidase activity is apparently not influenced by the incubation with HS, confirming the lack of something enhancing the reaction between the partners.
A multidisciplinary approach to study proteins-humic substances interactions
Grazia Masciandaro;Brunello Ceccanti;
2011
Abstract
Humic substances is a generic term to indicate relatively high molecular weight, brown to black colored substances formed by secondary condensation reactions, negatively charged, branched polyelectrolytes with mainly carboxylic and phenolic functional groups. Humic substances are ubiquitary in nature. The classical view of humic substances shares three basic fractions termed humic acids (soluble at alkaline pH values), fulvic acids (soluble at a wide range of pH values) and humine (insoluble in water at any pH). Considerable uncertainty still exists regarding the molecular weight and structure of humic substance. The main accepted model is the supramolecular structure, and regardless of their molecular structure, they constitute 70-80% of the soil organic matter. It is well kwon that proteins in the soil ecosystem interact with the solid phases, either inorganic (e.g. clays) or organic (e.g. humic acids). While interactions between proteins of various origin with clays has been widely studied, interactions between proteins and humic substances is considerably less characterized. Most of the information on this topic is based on the extraction of humic-enzymatic complexes, which have been proved to preserve the enzymes from chemical degradation or hydrolysis. To understand the modes of interactions between microbial proteins and humic substances, we undertook a multidisciplinary study based on the behaviour of humic substances of various origin, with a purified ?-glucosidase from the soil-borne fungus Aspergillus niger. Chemical interactions between the enzyme and humic substances was studied using a quartz microbalance (Kinetica, Elba Tech), which indicates the eventual formation of chemical bonds. Effects of the humic substances on the enzyme activity was studied through native gel electrophoresis and visualization of the enzyme activity by staining with 4-Methylumbelliferyl-beta-D-glucopyranoside. The preliminary results show that under the tested conditions, the formation of enzyme-humic substances complexes requires specific factors to occur, and that the ?-glucosidase activity is apparently not influenced by the incubation with HS, confirming the lack of something enhancing the reaction between the partners.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
