How do different pHs affect the action of the enzyme pancreatin?

Rebecca Brown 10BRG

I predict that the optimum pH for the enzyme pancreatin is pH 9. I came to this decision after taking into consideration the following information.

Catalysts speed up a reaction without being used up and so therefore they can be used over and over again. Due to them not being used up they are only required in very small amounts. Enzymes are biological catalysts and I will be using digestive enzymes for the experiment that I will be carrying out. The digestive juices contain enzymes, which break down large insoluble molecules into small soluble molecules. There are 3 main types of digestive enzymes and a different one is needed for each category of food. The enzymes which catalyse the breakdown of carbohydrates is carbohydrase; the enzymes which catalyse the breakdown of fats is lipase and the enzymes which catalyse the breakdown of protein is protease. Carbohydrates are broken down into glucose, fats are broken down into fatty acids (glycerol) and proteins are broken down into amino acids. Pancreatin contains a protease enzyme.

Enzymes are all proteins and they are affected by temperature and pH; they have an optimum. Enzymes work on substances called a substrate. Enzymes have very specific shapes; each enzyme only works on its own specific substrates. This can be explained by using the lock and key theory where the lock is the enzyme and the key is the substrate. Only the correct shape and sized substrate (key) can fit into the active site (keyhole) of the enzyme (lock). The substance made at the end is called the product.

Diagram from

The enzyme is held into the very specific 3D shape by different types of bonds. If these bonds become broken or damaged in any way then the active site could change shape and so therefore the substrate would no longer bind as tightly. The conditions that damage the bonds are temperature and pH. Enzymes have an optimum for both of these factors. If the optimum pH for an enzyme was pH8 and the pH of the surroundings was altered slightly this would cause some of the ionic bonds holding the enzyme in its shape to break. The same also goes for temperature. However, the shape would only become slightly changed and so therefore the enzyme would still work but just not as quickly as it would in the optimum pH and temperature.

On the other hand if the pH was altered a long way from the optimum this would then cause the shape to become more distorted and decreasing the chances of the substrate binding to the active site. This again also applies to temperature. When the substrate no longer fits into the active site we say that the enzyme has become denatured and so therefore can no longer be used in a reaction. This happens at high temperatures and extreme pHs.

The aim of my experiment is to find out the optimum pH for pancreatin. Conditions in the stomach are acidic (approximately pH2/3) because our stomach contains hydrochloric acid. There are two reasons as to why the conditions are like this

To kill any bacteria
It provides the correct conditions for the stomach protease.

Food is the passed down into the duodenum (the 1st part of the small intestine) which is where the digestion of food occurs. Pancreatin is secreted into the duodenum to carry on the breakdown of food. Bile (which is ...