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Extracellular enzymes or exoenzymes are synthesized inside the cell and then secreted outside the cell, where their function is to break down complex macromolecules into smaller units to be taken up by the cell for growth and assimilation. These enzymes degrade complex organic matter such as cellulose and hemicellulose into simple sugars that enzyme-producing organisms use as a source of carbon, energy, and nutrients. Grouped as hydrolases, lyases, oxidoreductases and transferases,〔 these extracellular enzymes control soil enzyme activity through efficient degradation of biopolymers. Upon senescence, plant residues, animals and microorganisms enter the dead organic matter pool and become a source of nutrients and energy for other organisms. Extracellular enzymes target macromolecules such as carbohydrates (cellulases), lignin (oxidases), organic phosphates (phosphatases), amino sugar polymers (chitinases) and proteins (proteases) and break them down into soluble sugars that are subsequently transported into cells to support heterotrophic metabolism.〔 Biopolymers are structurally complex and require the combined actions of a community of diverse microorganisms and their secreted exoenzymes to depolymerize the polysaccharides into easily assimilable monomers. These microbial communities are ubiquitous in nature, inhabiting both terrestrial and aquatic ecosystems. The cycling of elements from dead organic matter by heterotrophic soil microorganisms is essential for nutrient turnover and energy transfer in terrestrial ecosystems. Exoenzymes also aid digestion in the guts of ruminants, termites, humans and herbivores. By hydrolyzing plant cell wall polymers, microbes release energy that has the potential to be used by humans as biofuel. Other human uses include waste water treatment, composting and bioethanol production. ==Factors influencing extracellular enzyme activity== Extracellular enzyme production supplements the direct uptake of nutrients by microorganisms and is linked to nutrient availability and environmental conditions. The varied chemical structure of organic matter requires a suite of extracellular enzymes to access the carbon and nutrients embedded in detritus. Microorganisms differ in their ability to break down these different substrates and few organisms have the potential to degrade all the available plant cell wall materials. To detect the presence of complex polymers, some exoenzymes are produced constitutively at low levels, and expression is upregulated when the substrate is abundant. This sensitivity to the presence of varying concentrations of substrate allows fungi to respond dynamically to the changing availability of specific resources. Benefits of exoenzyme production can also be lost after secretion because the enzymes are liable to denature, degrade or diffuse away from the producer cell. Enzyme production and secretion is an energy intensive process and, because it consumes resources otherwise available for reproduction, there is evolutionary pressure to conserve those resources by limiting production. Thus, while most microorganisms can assimilate simple monomers, degradation of polymers is specialized, and few organisms can degrade recalcitrant polymers like cellulose and lignin. Each microbial species carries specific combinations of genes for extracellular enzymes and is adapted to degrade specific substrates.〔 In addition, the expression of genes that encode for enzymes is typically regulated by the availability of a given substrate. For example, presence of a low-molecular weight soluble substrate such as glucose will inhibit enzyme production by repressing the transcription of associated cellulose-degrading enzymes. Environmental conditions such as soil pH, soil temperature, moisture content, and plant litter type and quality have the potential to alter exoenzyme expression and activity. Variations in seasonal temperatures can shift metabolic needs of microorganisms in synchrony with shifts in plant nutrient requirements. Agricultural practices such as fertilizer amendments and tillage can change the spatial distribution of resources, resulting in altered exoenzyme activity in the soil profile. Introduction of moisture exposes soil organic matter to enzyme catalysis and also increases loss of soluble monomers via diffusion. Additionally, osmotic shock resulting from water potential changes can impact enzyme activities as microbes redirect energy from enzyme production to synthesizing osmolytes to maintain cellular structures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Extracellular enzymes or exoenzymes are synthesized inside the cell and then secreted outside the cell, where their function is to break down complex macromolecules into smaller units to be taken up by the cell for growth and assimilation. These enzymes degrade complex organic matter such as cellulose and hemicellulose into simple sugars that enzyme-producing organisms use as a source of carbon, energy, and nutrients. Grouped as hydrolases, lyases, oxidoreductases and transferases, these extracellular enzymes control soil enzyme activity through efficient degradation of biopolymers.Upon senescence, plant residues, animals and microorganisms enter the dead organic matter pool and become a source of nutrients and energy for other organisms. Extracellular enzymes target macromolecules such as carbohydrates (cellulases), lignin (oxidases), organic phosphates (phosphatases), amino sugar polymers (chitinases) and proteins (proteases) and break them down into soluble sugars that are subsequently transported into cells to support heterotrophic metabolism.Biopolymers are structurally complex and require the combined actions of a community of diverse microorganisms and their secreted exoenzymes to depolymerize the polysaccharides into easily assimilable monomers. These microbial communities are ubiquitous in nature, inhabiting both terrestrial and aquatic ecosystems. The cycling of elements from dead organic matter by heterotrophic soil microorganisms is essential for nutrient turnover and energy transfer in terrestrial ecosystems. Exoenzymes also aid digestion in the guts of ruminants, termites, humans and herbivores. By hydrolyzing plant cell wall polymers, microbes release energy that has the potential to be used by humans as biofuel. Other human uses include waste water treatment, composting and bioethanol production.==Factors influencing extracellular enzyme activity==Extracellular enzyme production supplements the direct uptake of nutrients by microorganisms and is linked to nutrient availability and environmental conditions. The varied chemical structure of organic matter requires a suite of extracellular enzymes to access the carbon and nutrients embedded in detritus. Microorganisms differ in their ability to break down these different substrates and few organisms have the potential to degrade all the available plant cell wall materials. To detect the presence of complex polymers, some exoenzymes are produced constitutively at low levels, and expression is upregulated when the substrate is abundant. This sensitivity to the presence of varying concentrations of substrate allows fungi to respond dynamically to the changing availability of specific resources. Benefits of exoenzyme production can also be lost after secretion because the enzymes are liable to denature, degrade or diffuse away from the producer cell.Enzyme production and secretion is an energy intensive process and, because it consumes resources otherwise available for reproduction, there is evolutionary pressure to conserve those resources by limiting production. Thus, while most microorganisms can assimilate simple monomers, degradation of polymers is specialized, and few organisms can degrade recalcitrant polymers like cellulose and lignin. Each microbial species carries specific combinations of genes for extracellular enzymes and is adapted to degrade specific substrates. In addition, the expression of genes that encode for enzymes is typically regulated by the availability of a given substrate. For example, presence of a low-molecular weight soluble substrate such as glucose will inhibit enzyme production by repressing the transcription of associated cellulose-degrading enzymes.Environmental conditions such as soil pH, soil temperature, moisture content, and plant litter type and quality have the potential to alter exoenzyme expression and activity. Variations in seasonal temperatures can shift metabolic needs of microorganisms in synchrony with shifts in plant nutrient requirements. Agricultural practices such as fertilizer amendments and tillage can change the spatial distribution of resources, resulting in altered exoenzyme activity in the soil profile. Introduction of moisture exposes soil organic matter to enzyme catalysis and also increases loss of soluble monomers via diffusion. Additionally, osmotic shock resulting from water potential changes can impact enzyme activities as microbes redirect energy from enzyme production to synthesizing osmolytes to maintain cellular structures.」の詳細全文を読む スポンサード リンク
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