Vitamin B12 is not produced by humans.
Methylmalonyl-CoA mutase ( MCM ) , mitochondrial , also known as methylmalonyl-CoA isomerase , is a protein that in humans is encoded by the MUT gene . Vitamin B12 . It is involved in the metabolism of every cell of the human body , especially affecting DNA synthesis , fatty acid and amino acid metabolism . No fungi , plants , or animals ( including humans ) are capable of producing vitamin B12 .