Tyrosinase inhibition due to interaction of homocyst(e)ine with copper: the mechanism for reversible hypopigmentation in homocystinuria due to cystathionine beta-synthase deficiency.

The study investigated the mechanism behind reversible hypopigmentation in patients with homocystinuria due to cystathionine beta-synthase deficiency. It was observed that two patients experienced darkening of their hypopigmented hair after treatment reduced plasma homocyst(e)ine levels. The researchers hypothesized that homocyst(e)ine inhibits tyrosinase, a key enzyme in pigmentation. Experiments showed that tyrosinase activity was reduced in the presence of homocysteine but could be restored by adding copper sulfate. This suggested that homocyst(e)ine interacts with copper at the active site of tyrosinase, leading to its inhibition and resulting in hypopigmentation. Other compounds like L-cystine and betaine did not affect tyrosinase activity, supporting the specific interaction between homocyst(e)ine and copper.