Methylmalonyl-CoA mutase is a mitochondrial homodimer apoenzyme (EC. 5. 4.99.2) that focuses on the catalysis of methylmalonyl CoA to succinyl CoA. The enzyme is bound to adenosylcobalamin, a hormonal derivative of vitamin B12 in order to function. Methylmalonyl-CoA mutase deficiency is caused by genetic defect in the MUT gene responsible for encoding the enzyme. Deficiency in this enzyme accounts for 60% of the cases of methylmalonic acidemia. Symptoms People with methylmalonyl CoA mutase deficiency exhibit many symptoms similar to other diseases involving inborn errors of metabolism. Newborn babies experience with vomiting, acidosis, hyperammonemia, hepatomegaly (enlarged livers), hyperglycinemia (high glycine levels), and hypoglycemia (low blood sugar). Later, cases of thrombocytopenia and neutropenia can occur. In some cases intellectual and developmental disabilities, such as autism, were noted with increased frequency in populations with methylmalonyl-CoA mutase deficiency. Causes Although methylmalonic acidemia has a variety of causes, both genetic and dietary, methylmalonyl CoA mutase deficiency is an autosomal recessive genetic disorder. Patients with the deficiency either have a complete gene lesion, designated as mut0 or a partial mutation in the form of a frameshift designated as mut-. This frameshift affects the folding of the enzyme rendering its binding domain less effective. Patients with a complete deletion have an inactivation of methylmalonyl CoA mutase and exhibit the most severe symptoms of the deficiency, while patients with a partial mutations have a wide range of symptoms. Over 49 different mutations have been discovered for the MUT gene, yet only two appear in any discernible frequency. Enzymatic activity Methylmalonyl-CoA mutase catalyzes the isomerization of methylmalonyl-CoA to succinyl-CoA, and uses a B12 derived prosthetic group, adenosylcobalamin, in order to accomplish this transfer. The enzyme is a homodimer, located in the mitochondrial matrix. The enzyme is 750 amino acids long, with the a metal ligand binding region to bind to the Cobalt region of adenosylcobalamin. The enzyme works by cleaving the adenosylcobalamin C-Co(III) bond, giving the carbon and cobalt (III) atoms each an electron. The cobalt then fluctuates between its two oxidation states: Co(II) and Co(III). In this way the adenosylcobalamin works as a reversible free radical generator. The cobalt therefore donates an electron back to the methylmalonyl-CoA backbone in order to transfer the coenzyme A group. Metabolic activity Methylmalonyl-CoA mutase is essential to the degradation pathways of many molecules including amino acids, and odd-chain fatty acids. Methylmalonyl-CoA mutase links the propionyl-CoA degradation byproduct of these macromolecules to the