An enzyme is a biological catalyst. Enzymes are composed of proteins, are specific to a particular reaction, and are generally named with the suffix -ase, for example "amalyase", which catalyses the break down of starch. Most enzymes work best at body temperature, and most will be damaged to the point at which they no longer work (i.e., become "denatured") at temperatures much higher than this. Strong acids or bases can also denature enzymes, as can heavy metals such as lead.