Problem:

I'm trying to obtain a better understanding of the Guthrie Test, which checks whether people have a disease called PKU. The Guthrie test uses bacteria to check for Phenylalanine (the amino acid) in blood samples. If both Phe and B-2-thienylalanine are available on the medium, the bacteria will grow. However, if only B-2-thienylalanine is available the bacteria will not grow.

In all of the articles I can find, I have seen no explanation, just a link to a paper that I can't find on the internet.: " A standard culture of Bacillus subtilis was incubated on agar in the presence of an antagonist of phenylalanine (B-2-thienylalanine), which prevents the bacteria from growing.3 " Link The reference they mention here is: "The inhibition assay: Its use in screening urinary specimens for metabolic differences associated with mental retardation" by R. Guthrie from 1960.

Required:

Question: Do we know what mechanism this protein is inhibiting?

Any help would be greatly appreciated.