Enzymes are large protein molecules which are vital in carrying out the chemical reactions responsible in maintaining homeostasis in our body systems. There are various factors which affects the functions of our enzymes. These factors include: enzyme concentration, substrate concentration, inhibitors, temperature, and pH (Voet and Voet, 2011). Given an adequate concentration of substrate, an increase in enzyme concentration will increase enzymatic reaction rates (Uddin, 2012). The relationship of substrate concentration to the function of enzyme is best explained by the Michaelis-Menten equation:
V1 = (Vmax [S])/( Km + [S])
where:
V1 = velocity at any time
[S] = substrate concentration at this time
Vmax = the maximum velocity under the set of factors (pH, temperature etc.)
Km = the Michaelis constant for the particular enzyme being investigated
The equation shows that the when the quantity of an enzyme is constant the reaction velocity is increased when the substrate concentration is increase. However, when the reaction velocity has reached its maximum point, any increase made in substrate concentration will not increase the reaction velocity (Udinn,2012; Voet and Voet; 2011; Worthington Biochemical Corporation, 2013). This is because the enzyme becomes saturated and all available enzymes have been converted to the enzyme substrate complex. The Michaelis constant Km is also defined as “the substrate concentration at ½ the maximum velocity of the enzyme.” The relationship among enzyme, substrate, and Michaelis constant (Km) could be summarized as follows: Km is directly proportional to the amount of enzyme required to saturate the substrate to achieve maximum velocity; and “that the substrate with the lowest Km upon which the enzyme acts as a catalyst is frequently assumed to be enzyme's natural substrate, though this is not true for all enzymes” (Worthington Biochemical Corporation, 2013).
Enzyme inhibitors are molecules which react to enzymes thereby reducing enzymatic activity. Inhibitors as compared to substrates do not react slowly with enzymes (Voet and Voet, 2011; Ophardt, 2003). These inhibitors may be categorized as: competitive (inhibitors competing with substrate); inactivator (inhibitors binding reversibly to enzymes); uncompetitive (inhibitors binding directly to enzyme-substrate complex but not to free enzyme); and mixed inhibitors (inhibitor binding to enzyme sites that participate in both substrate binding and catalysis) (Voet and Voet; 2011).
While, enzymatic reactions are proportional to temperature such that enzyme-catalyzed reaction increases when temperature rises, there is an optimal or a maximum temperature which limits the enzymes to function effectively (Uddin, 2012). Enzymes operate best that is at 5°C or below but not frozen. A relatively significant rise in temperature may cause the inactivation of enzyme. For instance, animal proteins become denatured at 40°C or even in moderate temperature (Worthington Biochemical Corporation, 2013). Aside from temperature, pH could also significantly affect enzymatic activities. Enzymes are known to be pH sensitive. That is, like temperature there is also an optimal pH condition where enzymes function best and any significant changes within the pH in the body chemistry can result to denaturation. According to Voet and Voet (2011) “most proteins are active only within the pH range of 5-9.” Voet and Voet (2011) further noted that enzymes only work at a narrow range of pH is due to the following factors: “the binding of substrate to enzyme; the catalytic activity; the ionization of substrate; and the variation of protein structure (usually significant only at extremes of pH).”
References
Ophardt, C. E. (2003). Enzymes. Elmhurst College: Virtual ChemBook. Retrieved from: http://www.elmhurst.edu/~chm/vchembook/573inhibit.html
Uddin, N. (2012). Interpolate the Rate of Enzymatic Reaction: Temperature, Substrate Concentration and Enzyme Concentration based Formulas using Newton’s Method. International Journal of Research in Biochemistry and Biophysics. 2(2): 5-9.
Voet, D. & Voet, J. G. (2011). Biochemistry. New Jersey: John Wiley & Sons, Inc.
Worthington Biochemical Corporation (2013). Introduction to Enzymes. New Jersey: Worthington Biochemical Corporation. Retrieved from: http://www.worthington-biochem.com/introbiochem/default.html
