Tyrosine is one of the 20 common amino acids found in all biological systems. It is catabolized as part of normal intermediary metabolism and in the breakdown of external proteins by soil microorganisms. Although it is not a xenobiotic compound, some of the intermediates of this pathway are also found in pathways for the catabolism of industrial and natural product aromatic ring compounds. One or more of these pathways are often found in Gram-positive and Gram-negative soil bacteria. In addition, Pseudomonas sp. strain CBS3 is able to convert 4-chlorophenylacetate to 3,4-dihydroxyphenylacetate. The latter merges into the pathway.