Substances that are altered by the action of proteases are known as
1) substrates
2)lipids
3)polysaccharides
4) phosphates

Substances that are altered by the action of proteases are known as: 1) substrates.

Explanation:

Protease is an enzyme, therefore a substrate would have to fit the enzyme, which forms an enzyme-substrate complex. This causes a chemical reaction since enzymes are biological catalysts. Many enzymes often change their shape so that the substrate can fit at the active site.

I hope this makes sense!! ^-^