If you look at the step where 5 methyl HTF enters the methylation cycle, it needs to interact with methylB12 to change homocysteine to methionine. This step always puzzles me bcos on the face of it, it looks like the cycle does not need the methyl group from folate becos methylb12 is already supplying the methyl group. So it looks like a transfer of the methyl group from 5 methylTHF to methyl B12 (which already has a methyl group). In other words, from most of the diagrams that I have seen, the rxn will go thru w/o the need for methylfolate or at least folate in its methyl form. I read somewhere that that methyl b12 'acts like a shuttle'. I don't know what that means. Further I have tried using formylfolate (folinic acid) before and the experience is very different. Some diagrams also have MTR as a catalyze/enzyme to this reaction ? What is that ? Also one more question can I assume that the uptake of methyl folate and methyl b12 in this cycle is 1:1 ? Thanks in advance.