Creatine kinase (ck), lactate dehydrogenase (ld), and aspartate transferase (ast) (formerly sgot) are examples of:

The three mentioned above are enzymes. Enzymes are proteins in our body that play a significant role in the metabolism. They are usually named ending with the syllable '-ase'. Enzymes are very role-specific. This means that there is a specific enzyme used to process nutrients that enter into our body and convert them further.