The Open Door Web Site

 

 BIOCHEMISTRY
 
FACTORS THAT AFFECT ENZYME ACTIVITY

Substrate concentration
Non-enzymic reactions
 The increase in velocity is proportional to the substrate concentration


.....
Enzymic reactions
 Are faster but they reach a saturation point when all the enzyme molecules are occupied.
 If you alter the concentration of the enzyme then Vmax will change too.

The effect of pH

Extreme pH levels will produce denaturation.
The structure of the enzyme is changed.
The active site is distorted and the substrate molecules will no longer fit in it.

At pH values slightly different from the enzyme’s optimum value, small changes in the charges of the enzyme and it’s substrate molecules will occur. This change in ionisation will affect the binding of the substrate with the active site.

Note: The pH at which the enzyme molecule’s charges are equal is called it’s isoelectric point. This corresponds to its optimum pH. On an electrophoresis gel the enzyme would not move as it has no overall charge at this pH.

The effect of temperature

Q10 (the temperature coefficient) = the increase in reaction rate with a 10°C rise in temperature.

For chemical reactions the Q10 = 2 to 3
(that is the rate of the reaction doubles or triples with every 10°C rise in temperature)

Enzyme-controlled reactions follow this rule as they are chemical reactions.

BUT at high temperatures proteins denature.

The optimum temperature for an enzyme controlled reaction will be a balance between the Q10 and denaturation.

For most enzymes the optimum temperature is about 30°C.
Many are a lot lower, cold water fish will die at 30°C because their enzymes denature.

A few bacteria have enzymes that can withstand very high temperatures up to 100°C.

Most enzymes however are fully denatured at 70°C.

© Paul Billiet 2008