Effects of Temperature and pH

An increase in temperature will increase the rate of non-enzyme-catalyzed reactions. A similar relationship between temperature and reaction rate occurs in enzyme-catalyzed reactions. At a temperature of 0° C the reaction rate is immeasurably slow. As the temperature is raised above 0° C the reaction rate increases, but only up to a point. At a few degrees above body temperature (which is 37° C) the reaction rate reaches a plateau; further increases in temperature actually decrease the rate of the reaction (fig. 4.3). This decrease is due to the fact that the tertiary structure of enzymes becomes altered at higher temperatures.

A similar relationship is observed when the rate of an enzymatic reaction is measured at different pH values. Each enzyme characteristically exhibits peak activity in a very narrow pH range, which is the pH optimum for the enzyme. If the pH is changed so that it is no longer within the enzyme's optimum range, the reaction rate will decrease (fig. 4.4). This decreased enzyme activity is due to changes in the conformation of the enzyme and in the charges of the R groups of the amino acids lining the active sites.

The pH optimum of an enzyme usually reflects the pH of the body fluid in which the enzyme is found. The acidic pH optimum of the protein-digesting enzyme pepsin, for example, allows it to be active in the strong hydrochloric acid of gastric juice. Similarly, the neutral pH optimum of salivary amylase and the alkaline pH optimum of trypsin in pancreatic juice allow these enzymes to digest starch and protein, respectively, in other parts of the digestive tract.

Although the pH of other body fluids shows less variation than that of the fluids of the digestive tract, the pH optima of different enzymes found throughout the body do show significant differences (table 4.3). Some of these differences can be exploited for diagnostic purposes. Disease of the prostate, for example, may be associated with elevated blood levels of a prostatic phosphatase with an acidic pH optimum (descriptively called acid phosphatase). Bone disease, on the other hand, may be associated with elevated blood levels of alkaline phosphatase, which has a higher pH optimum than the similar enzyme released from the diseased prostate.

Pepsin And Trypsin
10 20 30 37 40 100 Temperature (°C)

■ Figure 4.3 The effect of temperature on enzyme activity. This effect is measured by the rate of the enzyme-catalyzed reaction under standardized conditions as the temperature of the reaction is varied.

Pepsine Amylase Trypsine

■ Figure 4.4 The effect of pH on the activity of three digestive enzymes. Salivary amylase is found in saliva, which has a pH close to neutral; pepsin is found in acidic gastric juice, and trypsin is found in alkaline pancreatic juice.

© The McGraw-Hill Companies, 2003

Table 4 .3 pH Optima of Selected Enzymes


Reaction Catalyzed


Pepsin (stomach)

Digestion of protein


Acid phosphatase (prostate)

Removal of phosphate



Salivary amylase (saliva)

Digestion of starch


Lipase (pancreatic juice)

Digestion of fat


Alkaline phosphatase (bone)

Removal of phosphate



Trypsin (pancreatic juice)

Digestion of protein


Monoamine oxidase

Removal of amine group


(nerve endings)

from norepinephrine

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    Why is the ph of pancreatic fluid close to neutral?
    8 years ago
    What are the three enzymes found in saliva?
    8 years ago
  • sami
    How to measure rate of enzyme catalyzed reaction with amylase?
    8 years ago
  • mario herz
    What is the effect of temperature and ph on pepsin?
    8 years ago
  • sarah
    What are the different effects of temperature and ph on the digestion of protein and starch?
    8 years ago
  • Diamanda
    How does temperature affect salivary amylase rate of reaction?
    8 years ago
  • Roisin
    What is the optimum temperature for salivary amylase?
    8 years ago
  • Frodo
    What decreases the rate of an enzymecatalyzed reaction in the body?
    8 years ago
  • ameera
    How does temperature effect human trypsin?
    7 years ago
  • roman gray
    What is the rate of reaction for amylase under temprature of 0, 37, and 100 respectively?
    4 years ago
  • selina smallburrow
    Is it salivary amylase or trypsin has higher optimum pH?
    4 years ago
  • arja
    What is neutral PH of salivary amailase?
    4 years ago
  • Mark
    What is the optimum temperature of the enzyme present in saliva?
    4 years ago
  • anna
    What are the effects of ph on pancreatic lipase?
    4 years ago
  • Rosalinda
    Why salivary amylase is alkaline?
    3 years ago
  • Bo
    How does raising temperature affect the digestion of the starch?
    3 years ago
  • alonzo
    How does temperature affect saliva amylase activity?
    3 years ago
  • Senay
    What is the effect of very acidic ph on ptyalin activity?
    3 years ago
  • orla
    How does difference in ph will differ in optimum ph of amylase activity?
    3 years ago
  • Jan
    What are the effects of pepsin trypsin?
    3 years ago
  • alan
    Does pH and temperaturw have the same effect on salivary amylase?
    3 years ago
  • tekle eyob
    Does tempature and ph affect digestion of lipids and starches?
    3 years ago
  • fosca
    Does temperature affect enzyme activity?
    2 years ago
  • abelino gallo
    How ph affects the digestive activity?
    2 years ago
  • Jesse
    How does temperature affect the starch to enzyme digestion?
    2 years ago
  • bisirat
    Did low temperrature affect digestion of protein?
    2 years ago
  • laurence
    Which ph will favour action of pepsin and trypsin?
    2 years ago
  • scott
    What happen when salivary amylase treat at low temp and high temp?
    2 years ago
  • justin hill
    What is the optimal pH for pepsin and salivary amylaseWhy do they differ?
    2 years ago
    Does pepsin work at 40°C?
    2 years ago
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    2 years ago
    What effect is high temperatures on saliva?
    2 years ago
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    How the temperature of ph affects the rates of protein digestive?
    2 years ago
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    How does temperature and ph constrain physiology?
    2 years ago
  • Eija-Riitt
    How does temperature affect ph anatomy and physiology?
    2 years ago
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    What is the temperature of pancreatic juice?
    2 years ago
    Why is human amylase optimal temperature 25 degrees celsius?
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    Does teperature affect ph in the body?
    1 year ago
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    How to chang temperature in pepsin?
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    1 year ago
  • christin
    How does temperature affect body fluid ph?
    12 months ago
  • nahand hayward
    How graph shows ph affect the rate of protein digestion by pepsin?
    10 months ago
  • Jamie
    How the temperature and the presense of pepsin influence the rate of protein digestion?
    8 months ago
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    6 months ago
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    Does temperature affect protein digestion?
    4 months ago
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    2 months ago
    What temperature and pH promotes digestion of protein molecules?
    2 months ago
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    How does pH affect pepsin activity?
    2 months ago
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    How does ph and temperature affect enzymes in the human body?
    2 months ago
  • Sirpa L
    How does pH effect enzyme digestion of protein?
    2 months ago

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