No P5P is not a methyl donor. But it is crucial to making methylfolate (by making the methylene intermediate, riboflavin-5-p controls the final step), to making methionine with the methionine synthase enzyme, to making dopamine and serotonin. to making gaba, to breaking down glycogen, and to regulating the trans-sulfuration pathway. From experience if you use the sublingual from Source Naturals and place it under the upper lip and have it stay there for a long time (like methyl B12 sublinguals with Freddd protocol) then the equivalent dose is stronger than say a Solgar oral P5p supplement? The relative ratio? Dunno for sure by maybe 50-100% stronger from my best guessing.