The only methylation reaction that doesn't require SAMe is the conversion of its own by-product back to methionine. Once SAMe is created, important things happen. Scientists are aware that chemicals create free radicals that cause cancer. Scientists also know that cancer cells have abnormal methylation. The connection between abnormal methylation and free radicals was put together when researchers at Northwestern University showed that if you oxidize a little section of DNA, it causes abnormal methylation.
Free radicals attach themselves to nucleic acids and alter methylation.
Methylation is a biochemical process that starts with methionine. When methionine reacts with ATP, SAMe is formed. In methylation, these groups break off from SAMe to catalyze other reactions. The leftover product eventually becomes homocysteine, which can be toxic if not converted. B vitamins are necessary for the conversion of homocysteine.