There is increasingly strong evidence that methionine and Methionine/Cysteine ratio vs. Glycine/Serine ratio (and generally keeping sulfur containing amino acids SCAA's low) is similar, or may be to a large degree the reason behind CR life extension benefits, see:
Am J Physiol Regul Integr Comp Physiol. 2007 Sep;293(3):R1046-55. Epub 2007 Jun 13.
Skrovanek S, Valenzano MC, Mullin JM.
Source
The Lankenau Institute for Medical Research, 100 Lancaster Avenue, Wynnewood, PA 19096, USA.
Abstract
Restriction of sulfur-containing amino acids (SCAA) has been shown to elicit a similar increase in life span and decrease in age-related morbidity as caloric restriction. The singular importance of epithelial barrier function in both physiological homeostasis and prevention of inflammation raised the issue of examining the effect of SCAA restriction on epithelial tight junction structure and permeability. Using a well-described in vitro, epithelial model, the LLC-PK(1) renal epithelial cell line, we studied the effects of SCAA restriction in culture medium. Reduction of methionine by 90%, cysteine by 50%, and total elimination of cystine resulted in dramatically lower intracellular pools of these amino acids and their metabolite, taurine, but the intracellular pools of the non-SCAA were all elevated. Cell growth and differentiation were maintained, and both confluent cell density and transepithelial short circuit current were unaffected. Certain tight junctional proteins, such as occludin and claudins-1 and -2 were not altered. However, claudins-3 and -7 were significantly decreased in abundance, whereas claudins-4 and -5 were markedly increased in abundance. The functional result of these structural changes was improved barrier function, as evidenced by increased transepithelial electrical resistance and decreased transepithelial (paracellular) diffusion of D-mannitol.
This is just a small example. There is a ton of info about this on many threads in this great forum.
But then again, Cysteine (and NAC especially) has many life extending implications as well, such as increasing Glutathione see this thread with links to lots of abstracts/studies: http://www.longecity...athione-by-300/
So the question to me becomes, is the net net better to restrict Cysteine levels or not? Or is there a way to get the benefits of NAC for examples, while mitigating or removing Cysteine elsewhere, perhaps added Glycine/Serine? But then again, Glycie acts as a IGF (or at least GH) secretagogue.
Do we have a consensus on what the best approach is on reconciling all of this? I'm personally leaning toward dietary methionine restriction as much as possible (legumes, macadamia nuts, gelatin protein as it has no Menthionine) and then possibly adding only 600mg NAC/day? The positives of NAC seem to always be targeted at Glutathione uptick. Perhaps the better approach here would be liposomal Glutathione or RiboCeine?
Let's get some traction on his topic here as it seems to have two very hot topics among life-extensionists suggesting diametrically opposite things.