What Are Most Enzymes?

Enzymes are biological substances that alter (usually speed up) the rate of reaction. Almost all enzymes are proteins. They are specific in nature. This means that one enzyme can operate on only one kind of substrate. Proteases only break down proteins and lipase would only work on lipids. This is because the shape and structure of the active site of each enzyme is different and is complementary to the shape of the substrate (such as lipids and proteins).
Enzymes lower the activation energy required for the breakdown of a substance thus speeding up their breakdown. They are a major force in our digestive system.
Enzyme activity may depend on temperature, pH, concentration of substrate and the presence of other molecules (inhibitors or activators).
While some enzymes may function in their original form, some need other molecules to attach to them to become active. These molecules are not proteins and are inorganic such as metal ions.