1. Recycling of Homocysteine
Homocysteine is a toxic amino acid, which is normally well controlled through the liver with the help of
B vitamains which convert it to non-toxic amino acids, among them Methionine. But when these paths
are blocked, or unavailable, homocysteine builds up in body tissues. When given to test animals, it
induces the initial stages of arteriosclerosis.
When our body recycles homocysteine and turns into methionine, a so called methyl donor is needed.
Methyltetrahydrofolate is the methyl donor. This is the reaction:

2. MTHF is turned into THD when it gives away the methyl group. This methyl group goes to tetra hydro-
bio- pterin or 4 BH.

3. 4BH gets turned into q-pterinand this helps convert aromatic amino acids to ring-hydroxylated
derivatives e.g., phenylalanine (Phe) tyrosine (Tyr) using a tetrahydropterin as electron donor.
Remember norepinephrine and dopamine formation need this reaction.