Lactic acid fermentation converts pyruvate to lactate by lactate dehydrogenase. Insulin stimulates the activity of pyruvate dehydrogenase phosphatase. It activates pyruvate dehydrogenase phosphatase which in turn activates the pyruvate dehydrogenase complex. The accumulating pyruvate is converted to lactate by lactate dehydrogenase. Patients with glucose-6-phosphate dehydrogenase deficiency risk haemolysis. These both serve to inhibit pyruvate dehydrogenase activity. Elevated concentrations of the enzyme lactate dehydrogenase (LDH) may be detected. Reduction by lactate dehydrogenase produces lactate. Lewisite is a suicide inhibitor of the E3 component of pyruvate dehydrogenase. It binds to the D subunit of ATP synthase and NADH dehydrogenase. Isobutyl nitrite is poisonous to people with glucose-6-phosphate dehydrogenase deficiency. These ions can inhibit oxidative enzymes such as yeast alcohol dehydrogenase. It is an X-linked recessive disorder that results in defective glucose-6-phosphate dehydrogenase enzyme. Retinal is then reduced to retinol by the enzyme retinol dehydrogenase. The nickel-containing enzyme carbon monoxide dehydrogenase catalyses this process.