It interacts with monoamine oxidase inhibitors. Cyclobenzaprine has major contraindications with monoamine oxidase inhibitors (MAOIs). Tranylcypromine acts as a nonselective and irreversible inhibitor of monoamine oxidase. An enzyme called monoamine oxidase (MAO) breaks down neurotransmitters. GABA can also be synthesized from putrescine by diamine oxidase and aldehyde dehydrogenase. Additionally, myoglobin and mitochondrial cytochrome oxidase are affected. Ernst Zeller found iproniazid to be a potent monoamine oxidase inhibitor. Mutations in the MAOA gene results in monoamine oxidase deficiency, or Brunner syndrome. The glucose in the blood reacts with an enzyme electrode containing glucose oxidase (or dehydrogenase). Tropolone is a grape polyphenol oxidase inhibitor. The active metabolite of allopurinol is oxipurinol, which is also an inhibitor of xanthine oxidase. Isoniazid is a mild monoamine oxidase inhibitor(MAO-I). It produces oxidase, catalase, and urease. Here is a diagram highlighting the pathways catalyzed by xanthine oxidase. It is positive for catalase and oxidase reactions.