Enzymes are substrate specific.
There are over 2000 known enzymes, each of which is involved in one specific chemical reaction. Enzymes are also substrate specific. The enzyme protease (which breaks peptide bonds in proteins) will not work on starch (which is broken down by an enzyme amylase). Similarly lipase enzymes acts only on and digests them into fatty acids and glycerol. Specificity of different enzymes are determined by the shapes of their active sites. Active sites possess specific geometric shapes that fit with specific substrates.