So I was reviewing Tyrosine and Phenylalanine metabolism (according to this video) and maybe I'm missing something but in the first step, 1:

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Oxygen atom reacts with Phenylalanine to make up Tyrosine, but the remaining Oxygen atom reacts with what exactly to end up as H2O?


1 Answer 1


The remaining oxygen reacts with the cofactor (called tetrahydro biopterin) of the enzyme phenylalanine oxidase, which loses two hydrogens to become dihydro biopterin (the oxidized form of the co-factor):

Gerald Litwack Ph.D., in Human Biochemistry, 2018

As for why: this is a monooxygenase, and an alternative would be to have $\ce{H2O2}$ as a product, but that's a reactive oxygen species the cell is better off without.


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