In rare cases, however, the enzyme is still able to produce the reactive intermediate 1,2-epoxyphenyl acetic acid, but is unable to convert this intermediate to homogentisate. The intermediate then spontaneously reacts with glutathione to form 2-L-cystein-S-yl-1,4-dihydroxy-cyclohex-5-en-1-yl acetic acid (hawkinsin).
In rare instances, however, the enzyme can still produce the reactive compound 1,2-epoxyphenyl acetic acid, but is unable to convert it into homogentisate. The intermediate then reacts with glutathione to form hawkinsin.