methionine seems to really only act as a methyl donor or a source of sulfur for serine, which is the actual precursor to cysteine. cysteine is very important, in the production of taurine, glutathione and various other things. but, the two amino acids don't seem to play related roles at all. so, why does the rdi combine methionine + cysteine? it seems to be strictly as a source of sulfur...
serine seems to be synthesized in multiple ways, but what i want to find is some measurement for how much i need in my diet, as it seems to be the actual thing i need for cysteine, taurine and glutathione, not methionine. but, there seems to be a deficit of information on the topic.
i'm getting enough of both methioine & cysteine to meet the rdis, i'm just not convinced that the rdis actually mean anything, as they don't seem to have much to do with each other.