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Baldwin wrote: >My question is: How is the level of dopamine regulated? >Does dopamine inhibit tyrosine hydroxylase or does it inhibit the >expression of the enzyme? What is the specific mechanism for >the inhibition reaction? That is, what are the specific reactions >that accomplish the regulation? I am not a biochemist but I thought I can help to clarify the question by the following example: The biosynthesis of isoleucine from threonine (conversion of an amino acid to another) is a five-step pathway. Each step requires a specific enzyme. The first step is conversion of threonine to ketobutyrate and catalyzed by threonine dehydratase. However, the end product isoleucine inhibits threonine dehydratase, hence, the production of isoleucine is regulated. I believe Baldwin is looking for answers of similar type. Unfortunately, I am not able to locate any reference regarding regulations of dopamine. Lee (age 43, dx of PD:1990)