Microbial degradative enzymes, importance

All soil metabolic proce.sses are driven by enzymes. The main sources of enzymes in soil are roots, animals, and microorganisms the last are considered to be the most important (49). Once enzymes are produced and excreted from microbial cells or from root cells, they face harsh conditions most may be rapidly decomposed by organisms (50), part may be adsorbed onto soil organomineral colloids and possibly protected against microbial degradation (51), and a minor portion may stand active in soil solution (52). The fraction of extracellular enzyme activity of soil, which is not denaturated and/or inactivated through interactions with soil fabric (51), is called naturally stabilized or immobilized. Moreover, it has been hypothesized that immobilized enzymes have a peculiar behavior, for they might not require cofactors for their catalysis. 

Sulfonylureas are systemic herbicides absorbed by the foliage and roots. They act by inhibiting acetolactate synthase, a key enzyme in the biosynthesis of branched chain aminoacids." This results in stopping cell division and plant growth. The most important degradation pathways of sulfonylureas are chemical hydrolysis and microbial degradation. 

Among the various biological, chemical and physical phenomena involved in the microbial degradation of polymers the biocatalytic reaction at the solid surface of the usually hydrophobic material is assumed to play an important role in the overall process. Factors such as the chemical environment of the cleaved bonds, rigidity of the polymer chain, the molar mass of the polymer, adsorption and surface activation of the enzyme, removal and dissolution of scission products from the surface are often used to control the degradation process (Chandra and Rustgi, 1998 Huang et al, 1994). 

Conventionally, the first attribute known about an enzyme used to be its function, usually in a crude extract. This property was screened for in microbial cultures or in tissue samples. The crude extract was then purified to homogeneity and the protein subjected to biochemical studies to learn of its pH and T profiles, its pi and subunit composition, catalytically important residues, and other properties. Proteolytic digestion of the protein with subsequent Edman degradation led to the primary sequence, but no information on the secondary structures such as a-heli-ces and [5-sheets or the folding in three dimensions of the polypeptide chain. The primary sequence could have been used to deduct the gene sequence but, with the degeneration of the code, several possibilities for certain amino acids occur, which makes prediction of the gene sequence a risk. 

A major experimental issue to be addressed is the rate and means by which particles are hydrolyzed and solubilized to provide substrates for heterotrophic bacteria, and the role of free enzymes in this process. Burns (1982) reviewed the possible locations and origin of enzyme activities in soils, and particularly underscored the potential importance of enzyme-humic complexes in microbial catalysis of substrates. As Burns (1982) discussed, enzymes associated with soil particles or humic substances are not subject to the same biochemical and physical restraints as are enzymes newly produced by microbial cells. Soil-held (or sediment-held) enzymes may therefore play a catalytic trigger role in substrate degradation, providing critical signals about substrate availability to the local microbial community. The conceptual model presented by Vetter et al. (1998) suggested that release of free enzymes into the environment may in fact represent... 

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