4. One way to monitor the activity of salivary amylase is to use the reagent I₂ in KI. What is the
basis for the use of this reagent and how can it be used to monitor enzymatic activity using
spectrophotometry?
Iodine with only itself is not soluble in water, in which it reacts with potassium iodine to form
triiodide ion in a reversible reaction of the iodide ion from the potassium iodide with iodine.
Colored adsorption complex is formed when the polyiodide ions react with the helical chains of
the glucose residue of amylase which is blue-black in color. Iodine shows blue color complex
with the reaction with the maltose by hydrolysis of amylose by the enzyme amylase from the
saliva (Sapkota, 2020). In monitoring the enzymatic activity, the blue color complex indicates
low enzymatic activity since there is still the presence of starch (Oliveira et al. 2019; Sapkota
2020).
Sapkota, A. (2020, November 19). Iodine Test- Definition, Principle, Procedure, Result, Uses.
Microbe Notes. https://microbenotes.com/iodine-test/.
Oliveira, H. M., Pinheiro, A. Q., Fonseca, A. J. M., Cabrita, A. R. J., & Maia, M. R. G. (2019).
Flexible and expeditious assay for quantitative monitoring of alpha-amylase and
amyloglucosidase activities. MethodsX, 6, 246–258.
https://doi.org/10.1016/j.mex.2019.01.007
6. An alternative assay for enzyme activity involves the DNS reaction. What is the basis for this
reaction?
The DNS reaction which means dinitrosalicylic acid reaction tests for the presence of reducing
sugar. DNS is an aromatic compound which reacts with reducing sugars like maltose from the
hydrolysis of amylose to form 3-amino-5-nitrosalicylic acid (orange red) (Wang, n.d.). The
concentration of the reducing sugars can be determined by describing the intensity of the
coloration of the solution (Cynthialearnsthings, 2016). The DNS method can be used to
determine the enzymatic activity of salivary amylase since the DNS reacts with maltose from the
hydrolysis of amylose in which a reducing sugar (Ouellette & Rawn, 2015).
Cynthialearnsthings. (2016, July 18). DNS Assay. cynthialearnsthings.
https://cynthialearnsthings.wordpress.com/2016/07/13/dns-assay/.
Ouellette, R. J., & Rawn, J. D. (2015). Carbohydrates. Principles of Organic Chemistry, 343–
370. https://doi.org/10.1016/b978-0-12-802444-7.00013-6
Wang, N. S. (n.d.). Glucose Assay by Dinitrosalicylic Colorimetric Method. Glucose Assay.
https://user.eng.umd.edu/~nsw/ench485/lab4a.htm.