Amino acid-monoxygenase

Tyrosine is not an essential amino acid in animals because it is synthesized from phenylalanine in a hydroxylation reaction. The enzyme involved, phenylala-nine-4-monoxygenase, requires the coenzyme tetrahydrobiopterin (Section 14.3), a folic acid-like molecule derived from GTP. Because this reaction also is a first step in phenylalanine catabolism, it is discussed further in Chapter 15. 

Hydrophobic partitioning is, however, exploited in a variety of colunrn techniques. Shiman et al achieved a high purification of L-phenylalanine 4-monoxygenase (E.C. 1.14.16.1) by what can essentially be described as biospecific retention on a hydrophobic chromatographic matrix. In the presence of L-phenylalanine the enzyme bound strongly to phenyl-agarose but desorbed when the column was washed with buffer, free of the amino-acid. 

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