Listed below are some articles that are of great reference for those interested in examining protease activity and their relationships to carbon and nitrogen, as well as their characterization. Click on the titles to follow the article.

  1. 1. Proteolytic activity in soil: A review
  2. WHAT:This article reviews current knowledge on inputs, sources and regulation of protease activities in soils from different ecosystems, while exploring limitations to proteolysis and N mineralization.
  3. RESULTS:The research led to one of the conclusions that the certain important areas for future research include the regulation of proteolysis by low-molecular-weight organic compounds, including amino acids, sugars, flavonoids, plant hormones and siderophores, as well as the identification and characterization of proteinaceous protease inhibitors of plant and microbial origin in the soil. Further research is needed because the understanding of roles of extracellular plant root proteases in N nutrition is weak. Investigation of the regulation of soil proteolytic activities of different ecosystems, especially in terms of pollutant inputs and the impact of climate change, is needed as well. Assessments of protease inhibitor inputs to the soil, regulation of these inhibitors via naturally occurring soil organic compounds, and the interactions between soil organisms is needed too.
  4. IMPORTANCE: It discusses extracellular proteases and how they enter the soil via microbial production and other sources, including plant root exudates, animal excrements, decomposition processes and leaching from agro-industrial fertilizers, as well as the regulating factors of synthesis and activities of proteases in soil.




2. Regulation of extracellular protease activity in soil in response to different sources and concentrations of nitrogen and carbon

WHAT: The goal of this study was to better understand how carbon (C) and nitrogen N availability affects soil protease activity using several aerobic incubations with ammonium (NH4+) and proteins as N sources and cellulose as the main C source. Much of nitrogen (N) in soil is in the form of proteinaceous material and it's breakdown requires the activity of extracellular proteases and other decomposing enzymes.

RESULTS: Strong increase in protease activity was seen when proteins were added and it depended on the amount added and its solubility. Substrates induced protease synthesis. In this phase, the addition of glucose but not ammonium resulted in protease repression, showing the level of protease sdsnythesis was determined by the need for C rather than N. After a month, it was found that different concentrations of mineral N in soil solution had no direct effect on protease activity. However, in its stationary phase, protease activity was repressible by glucose and ammonium with limited N availability. Adding ammonium allowed for reallocation of C and N away from protease synthesis, which leads to the observed protease activity decrease. This repression by glucose may be from the shifts in the pathway accommodating ammonium.

IMPORTANCE: This article shows the close links between the microbially mediated cycles of organic C and N.



3. Characterization of humus protease complexes extracted from soil

WHAT: Pyrophosphate (140 mM, pH 7.1) extracts of two arable soils and one pasture soil were ultrafiltrated separating the extracted material into three fractions: AI with nominal molecular weight (nmw) > 100 kD, AII with nmw between 10 kD and 100 kD and R with nmw < 10 kD. Protease activity was determined in each by using three different substrates: N-benzoyl-l-argininamide (BAA), specific for trypsin; N-benzyloxy-carbonyl-l-phenylalanyl l-leucine (ZPL), specific for carboxypeptidases; and casein, essentially a non-specific substrate. The derivative fractions were analyzed for their amino acid N and humic (HA) and fulvic (FA) acid contents.

RESULTS: There was resistance to thermal denaturation in the extracted protease organic complexes and some of them showed optimal activity at pH values greater than 10 as a result of the polyanionic characteristics of the humic material surrounding enzyme molecules and of the presence of alkaline protease. Comparing data obtained in Py-GC analyses and in protease activity suggested that BAA-hydrolysing activity was associated to a highly condensed humic matter and ZPL-hydrolysing activity to less resistant humic substances when at least some of the extracted casein-hydrolysing activity was present as glycoproteins not associated to humus. Fresh organic matter of carbohydrate origin probably inhibited BAA-hydrolysing activity whereas lignin derived organic matter probably inhibited ZPL- and casein-hydrolysing activity.

IMPORTANCE: This article examines the extracts activities monitoring their thermal stability and the activities of the extract and derivative fractions for their optimal pH.


4. Relationship between carbon and nitrogen availability and extracellular enzyme activities in soil

WHAT: Microorganisms need extracellular enzymes to break down insoluble organic polymers like cellulose, protein, and chitin into smaller units for uptake. The objective of this study was to investigate factors affecting the relationship between soil extracellular enzyme activities and C and N turnover.

RESULTS: Incubations were carried out with ammonium and proteins as N sources and cellulose as the main C source. Cellulase was positively correlated with the amount added, as well as how much N was available. A decrease in the C to N ratio from 40 to 10 led to an increase in exocellulase and beta-glucosidase activity of 18% and 10%, respectively. Protease activity depended on the amount and kind of protein added, but an increase in carbon availability resulted in an elevated protease activity. At first, protease and cellulase activity were started up by their corresponding substrates, and an increase in activity of both enzymes resulted in a proportional increase in carbon dioxide evolution. Results later showed that enzyme activity became increasingly determined by the amount and kind of substrate availability, but N turnover became increasingly dominated by the C to N ratio of substrates added.

IMPORTANCE: This case showed that though enzyme activities by its self may not be sufficient to describe the decomposition process, they can give valuable information about the availability of specific organic compounds and their degradation over time.

Hopefully, these articles are helpful in understanding some of the protease activity relationships. View our other protease blogs to update your current knowledge on these proteolytic enzymes.



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