500
                                VItamin B12 status is dependent on vitamin B6 and folic acid. The elevated homocysteine could reflect a deficiency of dietary intake in one of any of these three nutrients. However, _____ is only found in vitamin B12 - specific pathway.  Therefore, the elevation of this acid and homocysteine level will help to confirm vitamin B12 deficiency.
                                What is methylmalonic acid (MMA).