Most enzymes are of protein nature. But there are some exceptions. For example, a few RNA molecules show some catalytic action. These RNA molecules are known as ribozymes. These are actually ribonucleoprotein particles, i.e., made up of protein and RNA, but only RNA portion shows catalytic activity. Example- RNase P in E. coli acts as an enzyme for catalysing the conversion of pre-tRNA to tRNA.